Currently the top level directory contains basically all of the code
for the crypto package. This PR moves the crypto code into submodules
in a similar manner to what `golang/x/crypto` does. This improves code
organization.

Ref discussion: https://github.com/tendermint/tendermint/pull/1966

Closes #1956

Signed-off-by: Silas Davis <silas@monax.io>

Signed-off-by: Silas Davis <silas@monax.io>

gogoproto.nullable compatible with GRPC downstream of ABCI and libs
protbuf types

We were computing these functions incorrectly.
I'm not sure what distribution these numbers are, but it isn't the
normal exponential distribution. (We're making the probability of
getting a number of a particular bitlength equal, but the number in
that bitlength thats gets chosen is uniformly chosen)

We weren't using these functions anywhere in our codebase, and they
had a nomenclature error. (There aren't exponentially distributed
integers, instead they would be geometrically distributed)

The godocs fell out of sync with the code here. Additionally we had
warning that these randomness functions weren't for cryptographic
use on every function. However these warnings are confusing, since
there was no implication that they would be secure there, and a
single warning on the actual Rand type would suffice. (This is what
is done in golang's math/rand godoc)

Additionally we indicated that rand.Bytes() was reading OS randomness
but in fact that had been changed.

This commit switches all usage of math/rand to cmn's rand. The only
exceptions are within the random file itself, the tools package, and the
crypto package. In tools you don't want it to lock between the go-routines.
The crypto package doesn't use it so the crypto package have no other
dependencies within tendermint/tendermint for easier portability.

Crypto/rand usage is unadjusted.

Closes #1343

Refs #693

This reverts commit d02c5d1e30.

closes https://github.com/tendermint/tmlibs/issues/133

This reverts commit 96a3502

Refs #1755

I started with writing a test for wsConnection (WebsocketManager) where
I:

- create a WS connection
- do a simple echo call
- close it

No leaking goroutines, nor any leaking memory were detected.

For useful shortcuts see my blog post
https://blog.cosmos.network/debugging-the-memory-leak-in-tendermint-210186711420

Then I went to the rpc tests to see if calling Subscribe results in
memory growth. It did.

I used a slightly modified version of TestHeaderEvents function:

```
func TestHeaderEvents(t *testing.T) {
	// memory heap before
	f, err := os.Create("/tmp/mem1.mprof")
	if err != nil {
		t.Fatal(err)
	}
	pprof.WriteHeapProfile(f)
	f.Close()

	for i := 0; i < 100; i++ {
		c := getHTTPClient()
		err = c.Start()
		require.Nil(t, err)

		evtTyp := types.EventNewBlockHeader
		evt, err := client.WaitForOneEvent(c, evtTyp, waitForEventTimeout)
		require.Nil(t, err)
		_, ok := evt.(types.EventDataNewBlockHeader)
		require.True(t, ok)

		c.Stop()
		c = nil
	}

	runtime.GC()

	// memory heap before
	f, err = os.Create("/tmp/mem2.mprof")
	if err != nil {
		t.Fatal(err)
	}
	pprof.WriteHeapProfile(f)
	f.Close()

	// dump all running goroutines
	time.Sleep(10 * time.Second)
	pprof.Lookup("goroutine").WriteTo(os.Stdout, 1)
}
```

```
Showing nodes accounting for 35159.16kB, 100% of 35159.16kB total
Showing top 10 nodes out of 48
      flat  flat%   sum%        cum   cum%
32022.23kB 91.08% 91.08% 32022.23kB 91.08%  github.com/tendermint/tendermint/libs/pubsub/query.(*QueryParser).Init
 1056.33kB  3.00% 94.08%  1056.33kB  3.00%  bufio.NewReaderSize
  528.17kB  1.50% 95.58%   528.17kB  1.50%  bufio.NewWriterSize
  528.17kB  1.50% 97.09%   528.17kB  1.50%  github.com/tendermint/tendermint/consensus.NewConsensusState
  512.19kB  1.46% 98.54%   512.19kB  1.46%  runtime.malg
  512.08kB  1.46%   100%   512.08kB  1.46%  syscall.ByteSliceFromString
         0     0%   100%   512.08kB  1.46%  github.com/tendermint/tendermint/consensus.(*ConsensusState).(github.com/tendermint/tendermint/consensus.defaultDecideProposal)-fm
         0     0%   100%   512.08kB  1.46%  github.com/tendermint/tendermint/consensus.(*ConsensusState).addVote
         0     0%   100%   512.08kB  1.46%  github.com/tendermint/tendermint/consensus.(*ConsensusState).defaultDecideProposal
         0     0%   100%   512.08kB  1.46%  github.com/tendermint/tendermint/consensus.(*ConsensusState).enterNewRound
```

100 subscriptions produce 32MB.

Again, no additional goroutines are running after the end of the test
(wsConnection readRoutine and writeRoutine both finishes). **It means
that some exiting goroutine or object is holding a reference to the
*Query objects, which are leaking.**

One of them is pubsub#loop. It's using state.queries to map queries to
clients and state.clients to map clients to queries.

Before this commit, we're not thoroughly cleaning state.queries, which
was the reason for memory leakage.

* expect all tags to be strings

Refs #1369

* port changes from https://github.com/tendermint/tmlibs/pull/204

Refs #1369

I had to alter events package for that. Hope that's fine.
Refs #847

Refs #847