* Implement better Parallel

We can make the implementation more robust by adjusting our assumptions
and leverage explicit file modes for syncing. Additionally we going to
assume that we want to clean up and can't really recover if thos
operations (file close and removal) fail.

* utilise file mode for majority of concerns
* improve test coverage by covering more assumptions
* signature parity with ioutil.WriteFile
* always clean up

Replaces #160

Fixes #134

Those functions are unused in the whole Tendermint Github
organization plus they were unnecessariy verbose and could
have been concisely replaced with

```go
func RightPadString(s string, totalLength uint) string {
       return fmt.Sprintf("% *s", totalLength, s)
}

func LeftPadString(s string, totalLength uint) string {
       return fmt.Sprintf("% -*s", totalLength, s)
}
```

delete them anyways

Fixes #169
Fixes https://github.com/tendermint/tendermint/issues/1322

The previous code was very trusting assuming that
rational actors will use this code. However, Byzantine
actors don't care and in the case of the linked issue
negative lengths can be sent to this code unfettered
having been received from a peer.

This code is essentially just a sign change from
`==`
to
`<=`

and we've gutted out that attack by being more defensive.

* common/random.go supports seeding and *Rand
* Ensure determinism

* encodeByteSlice uses uvarint for length instead of varint
* Implemented NewPrefixDB
* Fix flowrate test (#165)
* Complete implementation and fix tests
* Add tests for MemBatch Write[Sync]

remove deprecated QuitService

fix RepeatTimer memory leak (Refs #137)

* test case

* drain channels on reset

Leaking memory:
```
leaktest.go:144: leaktest: leaked goroutine: goroutine 116 [chan send]:
        github.com/tendermint/tmlibs/common.(*RepeatTimer).fireRoutine(0xc42006a410, 0xc4203403c0, 0xc42031b2c0)
                /go/src/github.com/tendermint/tmlibs/common/repeat_timer.go:160 +0x6e
        created by github.com/tendermint/tmlibs/common.(*RepeatTimer).reset
                /go/src/github.com/tendermint/tmlibs/common/repeat_timer.go:196 +0xe9
```

The alternative solution could be draining channels on the client side.

* add one more select instead of draining

thanks to Jae

Fixes https://github.com/tendermint/tmlibs/issues/145
Fixes https://github.com/tendermint/tmlibs/issues/146

The code in here has been fragile when it comes to nil
but these edge cases were never tested, although they've
showed up in the wild and were only noticed because
the reporter actually read the logs otherwise
we'd have never known.

This changes covers some of these cases and adds some tests.

IsHex should also successfully decode strings prefixed with
0X instead of only 0x strings.

Also add tests generally for IsHex.

Should fix a nondeterministic bug so...

Update previously only checked that the receiver was
non-nil but didn't check that the input parameter to update
"o" was non-nil causing a nil dereference in cases such as
fe632ea32a/consensus/reactor.go (L306)

Fixes https://github.com/tendermint/tendermint/issues/1169

* Canonical KVPair in common
* Simplify common/Bytes to just hex encode

Lesson articulated by @jaekwon on why we need 80 bits
of entropy at least before we can think of cryptographic
safety. math/rand's seed is a max of 64 bits so can never
be cryptographically secure.

Also added some benchmarks for RandBytes

Massive test simplication for more reliable tests from @ebuchman

Fixes https://github.com/tendermint/tmlibs/issues/99
Updates https://github.com/tendermint/tendermint/issues/973

Removed usages of math/rand.DefaultSource in favour of our
own source that's seeded with a completely random source
and is safe for use in concurrent in multiple goroutines.
Also extend some functionality that the stdlib exposes such as
* RandPerm
* RandIntn
* RandInt31
* RandInt63

Also added an integration test whose purpose is to be run as
a consistency check to ensure that our results never repeat
hence that our internal PRNG is uniquely seeded each time.
This integration test can be triggered by setting environment variable:
`TENDERMINT_INTEGRATION_TESTS=true`
for example
```shell
TENDERMINT_INTEGRATION_TESTS=true go test
```