The main change here is to use encoding/json to encode and decode RPC 
parameters, rather than the custom tmjson package. This includes:

- Update the HTTP POST handler parameter handling.
- Add field tags to 64-bit integer types to get string encoding (to match amino/tmjson).
- Add marshalers to struct types that mention interfaces.
- Inject wrappers to decode interface arguments in RPC handlers.

* Update Caller interface and its documentation.
* Rework MapToRequest as ParamsToRequest.

The old interface returned the result as well as populating it.  Nothing was
using this, so drop the duplicated value from the return signature. Clarify the
documentation on the Caller type.

Rework the MapToRequest helper to take an arbitrary value instead of only a
map. This is groundwork for getting rid of the custom marshaling code. For now,
however, the implementation preserves the existing behaviour for the map, until
we can replace those.

The code in the Tendermint repository makes heavy use of import aliasing.
This is made necessary by our extensive reuse of common base package names, and
by repetition of similar names across different subdirectories.

Unfortunately we have not been very consistent about which packages we alias in
various circumstances, and the aliases we use vary. In the spirit of the advice
in the style guide and https://github.com/golang/go/wiki/CodeReviewComments#imports,
his change makes an effort to clean up and normalize import aliasing.

This change makes no API or behavioral changes. It is a pure cleanup intended
o help make the code more readable to developers (including myself) trying to
understand what is being imported where.

Only unexported names have been modified, and the changes were generated and
applied mechanically with gofmt -r and comby, respecting the lexical and
syntactic rules of Go.  Even so, I did not fix every inconsistency. Where the
changes would be too disruptive, I left it alone.

The principles I followed in this cleanup are:

- Remove aliases that restate the package name.
- Remove aliases where the base package name is unambiguous.
- Move overly-terse abbreviations from the import to the usage site.
- Fix lexical issues (remove underscores, remove capitalization).
- Fix import groupings to more closely match the style guide.
- Group blank (side-effecting) imports and ensure they are commented.
- Add aliases to multiple imports with the same base package name.

Migrates the `rpc` package to use new JSON encoder in #4955. Branched off of that PR.

Tests pass, but I haven't done any manual testing beyond that. This should be handled as part of broader 0.34 testing.

Closes https://github.com/tendermint/tendermint/issues/3857

Moves `lib/` folder to `jsonrpc/`.

Renames:

**packages**

`rpc` package -> `jsonrpc` package
`rpcclient` package -> `client` package
`rpcserver` package -> `server` package

**structs and interfaces**

```
JSONRPCClient to Client
JSONRPCRequestBatch to RequestBatch
JSONRPCCaller to Caller
```

**functions**

```
StartHTTPServer to Serve
StartHTTPAndTLSServer to ServeTLS

rpc/jsonrpc/client: rename NewURIClient to NewURI

NewJSONRPCClient to New
NewJSONRPCClientWithHTTPClient to NewWithHTTPClient
NewWSClient to NewWS
```

**misc**

- unexpose `ResponseWriterWrapper`
- remove unused http_params.go

Closes #4603

Commands used (VIM):

```
:args `rg -l errors.Wrap`
:argdo normal @q | update
```

where q is a macros rewriting the `errors.Wrap` to `fmt.Errorf`.

https://www.jsonrpc.org/specification

What is done in this PR:

    JSONRPCClient: validate that Response.ID matches Request.ID I wanted
    to do the same for the WSClient, but since we're sending events as
    responses, not notifications, checking IDs would require storing
    them in memory indefinitely (and we won't be able to remove them
    upon client unsubscribing because ID is different then).

    Request.ID is now optional. Notification is a Request without an ID.
    Previously "" or 0 were considered as notifications

    Remove #event suffix from ID from an event response (partially fixes
    #2949) ID must be either string, int or null AND must be equal to
    request's ID. Now, because we've implemented events as responses, WS
    clients are tripping when they see Response.ID("0#event") !=
    Request.ID("0"). Implementing events as requests would require a lot
    of time (~ 2 days to completely rewrite WS client and server)

    generate unique ID for each request

    switch to integer IDs instead of "json-client-XYZ"
    id=0 method=/subscribe
    id=0 result=...
    id=1 method=/abci_query
    id=1 result=...

> send events (resulting from /subscribe) as requests+notifications (not
responses)

this will require a lot of work. probably not worth it

* rpc: generate an unique ID for each request
in conformance with JSON-RPC spec

* WSClient: check for unsolicited responses

* fix golangci warnings

* save commit

* fix errors

* remove ID from responses from subscribe
Refs #2949

* clients are safe for concurrent access

* tm-bench: switch to int ID

* fixes after my own review

* comment out sentIDs in WSClient
see commit body for the reason

* remove body.Close
it will be closed automatically

* stop ws connection outside of write/read routines
also, use t.Rate in tm-bench indexer when calculating ID

fix gocritic issues

* update swagger.yaml

* Apply suggestions from code review

* fix stylecheck and golint linter warnings

* update changelog

* update changelog2