`abci.Client`:

- Sync and Async methods now accept a context for cancellation
    * grpc client uses context to cancel both Sync and Async requests
    * local client ignores context parameter
    * socket client uses context to cancel Sync requests and to drop Async requests before sending them if context was cancelled prior to that

- Async methods return an error
    * socket client returns an error immediately if queue is full for Async requests
    * local client always returns nil error
    * grpc client returns an error if context was cancelled before we got response or the receiving queue had a space for response (do not confuse with the sending queue from the socket client)

- specify clients semantics in [doc.go](https://raw.githubusercontent.com/tendermint/tendermint/27112fffa62276bc016d56741f686f0f77931748/abci/client/doc.go)

`mempool.TxInfo`

- add optional `Context` to `TxInfo`, which can be used to cancel `CheckTx` request

Closes #5190

Remove Response/Request SetOption from ABCI.

Co-authored-by: Anton Kaliaev <anton.kalyaev@gmail.com>

## Description

Enable errcheck linter throughout the codebase

Closes: #5059

## Description

Work towards enabling errcheck

ref #5059

* New lint version upgrade

- linter was upgraded

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* enable-a;; is deprecated

* minor change

* another try

* some more changes

* some more changes

* reenable prealloc

* add version till bot is fixed

* Update makefile

- these two files were taken from the sdk with adjustments for usage in TM

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* .phony

* remove slate

* more tools

* circleci update 1/2

* fixed typo

* fixed bash error

* '<<' must be escaped in 2.1

* fixed invalid config

* removed golangci-lint from tools. runs as github app now

* one more issue in Circle config

* some more work on the Circle config

* minor changes

* fiddling with restore cache config

* fiddling with restore cache config

* added commands in circle config. makefile changes

* bash shenannigans

* bash shenannigans

* fighting the config demons

* fighting the config demons, v2

* fighting the config demons, v3

* updating p2p dockerfile

* updating p2p dockerfile

* updating p2p test

* updating p2p test

* testing circle config

* testing circle config

* remove dontcover command

* its the weekend, custom docker image

As per #2127, this refactors the RequestCheckTx ProtoBuf struct to allow for a flag indicating whether a query is a recheck or not (and allows for possible future, more nuanced states).

In order to pass this extended information through to the ABCI app, the proxy.AppConnMempool (and, for consistency, the proxy.AppConnConsensus) interface seems to need to be refactored along with abcicli.Client.

And, as per this comment, I've made the following modification to the protobuf definition for the RequestCheckTx structure:

enum CheckTxType {
  New = 0;
  Recheck = 1;
}

message RequestCheckTx {
  bytes tx = 1;
  CheckTxType type = 2;
}

* Refactor ABCI CheckTx to notify of recheck

As per #2127, this refactors the `RequestCheckTx` ProtoBuf struct to allow for:

1. a flag indicating whether a query is a recheck or not (and allows for
   possible future, more nuanced states)
2. an `additional_data` bytes array to provide information for those more
   nuanced states.

In order to pass this extended information through to the ABCI app, the
`proxy.AppConnMempool` (and, for consistency, the
`proxy.AppConnConsensus`) interface seems to need to be refactored.

Commits:

* Fix linting issue

* Add CHANGELOG_PENDING entry

* Remove extraneous explicit initialization

* Update ABCI spec doc to include new CheckTx params

* Rename method param for consistency

* Rename CheckTxType enum values and remove additional_data param

* Update to using go mod from dep

* Remove references to make get_vendor_deps

* Specify go version

* Set GO111MODULE=on and add -mod=readonly

* Fix exported env

* switch to using go1.12 everywhere

* Fix test scripts

* Typo:

* Prepend GO111MODULE=on

* remove dep cache

* Revert "remove dep cache"

This reverts commit 45117bda

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* bring back the dependency cache and change it to cache modules instead
of vendored deps; also:

 - bump version for dependency cache
 - bump version on pkg-cache (includes modules directory)

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* remove some more traces of dep:
 - remove Gopkg.(toml | lock)
 - update contributing guidlines
 - set global default in circleci (GO111MODULE=on)

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* global var failed for `test_cover` with
`go: unknown environment setting GO111MODULE=true`
although the var was `GO111MODULE: on`

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* Changelog pending entry

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* Add bbolt dependency to go.mod

Signed-off-by: Ismail Khoffi <Ismail.Khoffi@gmail.com>

* move -mod=readonly to build flags

This PR changes ABCI time format from int64 (Unix seconds) to WKT (WellKnownType) google.protobuf.Timestamp.

Refs #1857

Reasons:

better precision
standard DT for proto

* update Gopkg.lock
* [makefile] remove extra grep
    - go list excludes vendor by default now
* proto3 timestamp
* [docs/abci-spec] note about serialisation format
* make time non-nullable

This reverts commit d02c5d1e30.