Continues from #3280 in building support for batched requests/responses in the JSON RPC (as per issue #3213).

* Add JSON RPC batching for client and server

As per #3213, this adds support for [JSON RPC batch requests and
responses](https://www.jsonrpc.org/specification#batch).

* Add additional checks to ensure client responses are the same as results

* Fix case where a notification is sent and no response is expected

* Add test to check that JSON RPC notifications in a batch are left out in responses

* Update CHANGELOG_PENDING.md

* Update PR number now that PR has been created

* Make errors start with lowercase letter

* Refactor batch functionality to be standalone

This refactors the batching functionality to rather act in a standalone
way. In light of supporting concurrent goroutines making use of the same
client, it would make sense to have batching functionality where one
could create a batch of requests per goroutine and send that batch
without interfering with a batch from another goroutine.

* Add examples for simple and batch HTTP client usage

* Check errors from writer and remove nolinter directives

* Make error strings start with lowercase letter

* Refactor examples to make them testable

* Use safer deferred shutdown for example Tendermint test node

* Recompose rpcClient interface from pre-existing interface components

* Rename WaitGroup for brevity

* Replace empty ID string with request ID

* Remove extraneous test case

* Convert first letter of errors.Wrap() messages to lowercase

* Remove extraneous function parameter

* Make variable declaration terse

* Reorder WaitGroup.Done call to help prevent race conditions in the face of failure

* Swap mutex to value representation and remove initialization

* Restore empty JSONRPC string ID in response to prevent nil

* Make JSONRPCBufferedRequest private

* Revert PR hard link in CHANGELOG_PENDING

* Add client ID for JSONRPCClient

This adds code to automatically generate a randomized client ID for the
JSONRPCClient, and adds a check of the IDs in the responses (if one was
set in the requests).

* Extract response ID validation into separate function

* Remove extraneous comments

* Reorder fields to indicate clearly which are protected by the mutex

* Refactor for loop to remove indexing

* Restructure and combine loop

* Flatten conditional block for better readability

* Make multi-variable declaration slightly more readable

* Change for loop style

* Compress error check statements

* Make function description more generic to show that we support different protocols

* Preallocate memory for request and result objects

I think it's nice when the Client interface has all the methods. If someone does not need a particular method/set of methods, she can use individual interfaces (e.g. NetworkClient, MempoolClient) or write her own interface.

technically breaking

Fixes #3458

* limit number of /subscribe clients and queries per client

Add the following config variables (under [rpc] section):
  * max_subscription_clients
  * max_subscriptions_per_client
  * timeout_broadcast_tx_commit

Fixes #2826

new HTTPClient interface for subscriptions

finalize HTTPClient events interface

remove EventSubscriber

fix data race

```
WARNING: DATA RACE
Read at 0x00c000a36060 by goroutine 129:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:168 +0x1f0

Previous write at 0x00c000a36060 by goroutine 132:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:191 +0x4e0
  github.com/tendermint/tendermint/rpc/client.WaitForOneEvent()
      /go/src/github.com/tendermint/tendermint/rpc/client/helpers.go:64 +0x178
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:139 +0x298
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162

Goroutine 129 (running) created at:
  github.com/tendermint/tendermint/rpc/client.(*Local).Subscribe()
      /go/src/github.com/tendermint/tendermint/rpc/client/localclient.go:164 +0x4b7
  github.com/tendermint/tendermint/rpc/client.WaitForOneEvent()
      /go/src/github.com/tendermint/tendermint/rpc/client/helpers.go:64 +0x178
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync.func1()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:139 +0x298
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162

Goroutine 132 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:878 +0x659
  github.com/tendermint/tendermint/rpc/client_test.TestTxEventsSentWithBroadcastTxSync()
      /go/src/github.com/tendermint/tendermint/rpc/client/event_test.go:119 +0x186
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162
==================
```

lite client works (tested manually)

godoc comments

httpclient: do not close the out channel

use TimeoutBroadcastTxCommit

no timeout for unsubscribe

but 1s Local (5s HTTP) timeout for resubscribe

format code

change Subscribe#out cap to 1

and replace config vars with RPCConfig

TimeoutBroadcastTxCommit can't be greater than rpcserver.WriteTimeout

rpc: Context as first parameter to all functions

reformat code

fixes after my own review

fixes after Ethan's review

add test stubs

fix config.toml

* fixes after manual testing

- rpc: do not recommend to use BroadcastTxCommit because it's slow and wastes
Tendermint resources (pubsub)
- rpc: better error in Subscribe and BroadcastTxCommit
- HTTPClient: do not resubscribe if err = ErrAlreadySubscribed

* fixes after Ismail's review

* Update rpc/grpc/grpc_test.go

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

* green pubsub tests :OK:

* get rid of clientToQueryMap

* Subscribe and SubscribeUnbuffered

* start adapting other pkgs to new pubsub

* nope

* rename MsgAndTags to Message

* remove TagMap

it does not bring any additional benefits

* bring back EventSubscriber

* fix test

* fix data race in TestStartNextHeightCorrectly

```
Write at 0x00c0001c7418 by goroutine 796:
  github.com/tendermint/tendermint/consensus.TestStartNextHeightCorrectly()
      /go/src/github.com/tendermint/tendermint/consensus/state_test.go:1296 +0xad
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162

Previous read at 0x00c0001c7418 by goroutine 858:
  github.com/tendermint/tendermint/consensus.(*ConsensusState).addVote()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:1631 +0x1366
  github.com/tendermint/tendermint/consensus.(*ConsensusState).tryAddVote()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:1476 +0x8f
  github.com/tendermint/tendermint/consensus.(*ConsensusState).handleMsg()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:667 +0xa1e
  github.com/tendermint/tendermint/consensus.(*ConsensusState).receiveRoutine()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:628 +0x794

Goroutine 796 (running) created at:
  testing.(*T).Run()
      /usr/local/go/src/testing/testing.go:878 +0x659
  testing.runTests.func1()
      /usr/local/go/src/testing/testing.go:1119 +0xa8
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162
  testing.runTests()
      /usr/local/go/src/testing/testing.go:1117 +0x4ee
  testing.(*M).Run()
      /usr/local/go/src/testing/testing.go:1034 +0x2ee
  main.main()
      _testmain.go:214 +0x332

Goroutine 858 (running) created at:
  github.com/tendermint/tendermint/consensus.(*ConsensusState).startRoutines()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:334 +0x221
  github.com/tendermint/tendermint/consensus.startTestRound()
      /go/src/github.com/tendermint/tendermint/consensus/common_test.go:122 +0x63
  github.com/tendermint/tendermint/consensus.TestStateFullRound1()
      /go/src/github.com/tendermint/tendermint/consensus/state_test.go:255 +0x397
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:827 +0x162
```

* fixes after my own review

* fix formatting

* wait 100ms before kicking a subscriber out

+ a test for indexer_service

* fixes after my second review

* no timeout

* add changelog entries

* fix merge conflicts

* fix typos after Thane's review

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

* reformat code

* rewrite indexer service in the attempt to fix failing test

https://github.com/tendermint/tendermint/pull/3227/#issuecomment-462316527

* Revert "rewrite indexer service in the attempt to fix failing test"

This reverts commit 0d9107a098.

* another attempt to fix indexer

* fixes after Ethan's review

* use unbuffered channel when indexing transactions

Refs https://github.com/tendermint/tendermint/pull/3227#discussion_r258786716

* add a comment for EventBus#SubscribeUnbuffered

* format code

* first commit

finalize rebase

add protoc_merkle to Makefile

* in progress

* fix kvstore

* fix tests

* remove iavl dependency

* fix tx_test

* fix test_abci_cli

fix test_apps

* fix test_apps

* fix test_cover

* rm rebase residue

* address comment in progress

* finalize rebase

* libs: Remove usage of custom Fmt, in favor of fmt.Sprintf

Closes #2193

* Fix bug that was masked by custom Fmt!

This reverts commit d02c5d1e30.

This reverts commit 96a3502

* all: gofmt

Run 'gofmt -w .' from project root.

* Update changelog to say that I ran gofmt

* Revert "Update changelog to say that I ran gofmt"

This reverts commit 956f133ff0.

Refs #847

Refs #909

Refs #1296

1. remove pointer
2. add Quit() method to Service interface

Expose it in rpc client
Move ABCIResults into tendermint/types from tendermint/state

uint64 is considered dangerous. the details will follow in a blog post.

See https://github.com/tendermint/tmlibs/issues/45

comment out failing consensus tests for now

rewrite rpc httpclient to use new pubsub package

import pubsub as tmpubsub, query as tmquery

make event IDs constants
EventKey -> EventTypeKey

rename EventsPubsub to PubSub

mempool does not use pubsub

rename eventsSub to pubsub

new subscribe API

fix channel size issues and consensus tests bugs

refactor rpc client

add missing discardFromChan method

add mutex

rename pubsub to eventBus

remove IsRunning from WSRPCConnection interface (not needed)

add a comment in broadcastNewRoundStepsAndVotes

rename registerEventCallbacks to broadcastNewRoundStepsAndVotes

See https://dave.cheney.net/2014/03/19/channel-axioms

stop eventBuses after reactor tests

remove unnecessary Unsubscribe

return subscribe helper function

move discardFromChan to where it is used

subscribe now returns an err

this gives us ability to refuse to subscribe if pubsub is at its max
capacity.

use context for control overflow

cache queries

handle err when subscribing in replay_test

rename testClientID to testSubscriber

extract var

set channel buffer capacity to 1 in replay_file

fix byzantine_test

unsubscribe from single event, not all events

refactor httpclient to return events to appropriate channels

return failing testReplayCrashBeforeWriteVote test

fix TestValidatorSetChanges

refactor code a bit

fix testReplayCrashBeforeWriteVote

add comment

fix TestValidatorSetChanges

fixes from Bucky's review

update comment [ci skip]

test TxEventBuffer

update changelog

fix TestValidatorSetChanges (2nd attempt)

only do wg.Done when no errors

benchmark event bus

create pubsub server inside NewEventBus

only expose config params (later if needed)

set buffer capacity to 0 so we are not testing cache

new tx event format: key = "Tx" plus a tag {"tx.hash": XYZ}

This should allow to subscribe to all transactions! or a specific one
using a query: "tm.events.type = Tx and tx.hash = '013ABF99434...'"

use TimeoutCommit instead of afterPublishEventNewBlockTimeout

TimeoutCommit is the time a node waits after committing a block, before
it goes into the next height. So it will finish everything from the last
block, but then wait a bit. The idea is this gives it time to hear more
votes from other validators, to strengthen the commit it includes in the
next block. But it also gives it time to hear about new transactions.

waitForBlockWithUpdatedVals

rewrite WAL crash tests

Task:
test that we can recover from any WAL crash.

Solution:
the old tests were relying on event hub being run in the same thread (we
were injecting the private validator's last signature).

when considering a rewrite, we considered two possible solutions: write
a "fuzzy" testing system where WAL is crashing upon receiving a new
message, or inject failures and trigger them in tests using something
like https://github.com/coreos/gofail.

remove sleep

no cs.Lock around wal.Save

test different cases (empty block, non-empty block, ...)

comments

add comments

test 4 cases: empty block, non-empty block, non-empty block with smaller part size, many blocks

fixes as per Bucky's last review

reset subscriptions on UnsubscribeAll

use a simple counter to track message for which we panicked

also, set a smaller part size for all test cases

callback gives more power to the publisher. plus it is optional
comparing to a channel, which will block the whole client if you won't
read from it.

* rpc: subscribe on reconnection

* rpc: fix unit tests

What's new:
- auto reconnect
- ping/pong
- colored tests