Currently IsDirEmpty returns true, err if it encounters
any error after trying to os.Open the directory.
I noticed this while studying the code and recalled a bug
from an earlier project in which doing the exact same thing
on code without permissions would trip out and falsely report
that the directory was empty.
Given demo.go in https://play.golang.org/p/vhTPU2RiCJ

* Demo:
```shell
$ mkdir -p sample-demo/1 && touch sample-demo/2
$ echo "1st round" && go run demo.go sample-demo
$ sudo chown root sample-demo && sudo chmod 0700 sample-demo
$ echo "2nd round" && go run demo.go sample-demo
```

That then prints out
```shell
1st round
original:: empty: false err: <nil>
updated::  empty: false err: <nil>
2nd round
original:: empty: true err: open data/: permission denied
updated::  empty: false err: open data/: permission denied
```

where in "2nd round", the original code falsely reports that
the directory is empty but that's a permission error.

I could write a code test for it, but that test requires me to change
users and switch to root as a Go user so no point in complicating our
tests, but otherwise it is a 1-to-1 translation between shell and Go.

http: http-utils added after extraction

Found common http utils that were being multiply duplicated across
many libraries and since am moving things in basecoin/unstable to
add for more functionality, it's better to put them in one
place.

Utilities and tests added:
- [X] FparseJSON
- [X] FparseAndValidateJSON
- [X] ParseRequestJSON
- [X] ParseAndValidateRequestJSON
- [X] WriteCode
- [X] WriteError
- [X] WriteSuccess
- [X] ErrorResponse

During review from @ethanfrey, made updates:
* Removed tt.want since it was a distraction/artifact that made
the reviewer think the tests weren't testing for both failed
and passed results.
* Added ErrorWithCode as WithCode is a common options pattern
in Go that could cause confusion:
  ErrorWithCode(error, int) ErrorResponse
* Using json.NewDecoder(io.Reader) error instead of
ioutil.ReadAll(io.Reader) to slurp all the bytes.
* Added more test scenarios to achieve 100% coverage of http.go

We use WriteFileAtomic in two places:

```
p2p/addrbook.go
338:    err = cmn.WriteFileAtomic(filePath, jsonBytes, 0644)

types/priv_validator.go
162:    err = WriteFileAtomic(privVal.filePath, jsonBytes, 0600)
```

and we don't need .bak in any of the above. We save priv_validator every
10ms and addrbook every 2 min.

The problem with {filePath}.new is that it is not safe for concurrent
use! Calling this function with the same params results in the following
error:

```
panic: Panicked on a Crisis: rename /root/.tendermint_test/consensus_replay_test/priv_validator.json.new /root/.tendermint_test/consensus_replay_test/priv_validator.json: no such file or directory

goroutine 47860 [running]:
github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common.PanicCrisis(0xcba800, 0xc42152d640)
	/go/src/github.com/tendermint/tendermint/vendor/github.com/tendermint/tmlibs/common/errors.go:33 +0x10f
github.com/tendermint/tendermint/types.(*PrivValidator).save(0xc42235f2c0)
	/go/src/github.com/tendermint/tendermint/types/priv_validator.go:165 +0x159
github.com/tendermint/tendermint/types.(*PrivValidator).signBytesHRS(0xc42235f2c0, 0x6, 0x0, 0xc424e88f03, 0xc429908580, 0xca, 0x155, 0x80, 0xc424e88f00, 0x7f4ecafc88d0, ...)
	/go/src/github.com/tendermint/tendermint/types/priv_validator.go:249 +0x2bb
github.com/tendermint/tendermint/types.(*PrivValidator).SignVote(0xc42235f2c0, 0xc4228c7460, 0xf, 0xc424e88f00, 0x0, 0x0)
	/go/src/github.com/tendermint/tendermint/types/priv_validator.go:186 +0x1a2
github.com/tendermint/tendermint/consensus.(*ConsensusState).signVote(0xc424efd520, 0xc400000002, 0xc422d5e3c0, 0x14, 0x20, 0x1, 0xc4247b6560, 0x14, 0x20, 0x0, ...)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:1556 +0x35e
github.com/tendermint/tendermint/consensus.(*ConsensusState).signAddVote(0xc424efd520, 0x2, 0xc422d5e3c0, 0x14, 0x20, 0x1, 0xc4247b6560, 0x14, 0x20, 0xc42001b300)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:1568 +0x200
github.com/tendermint/tendermint/consensus.(*ConsensusState).enterPrecommit(0xc424efd520, 0x6, 0x0)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:1082 +0x13a4
github.com/tendermint/tendermint/consensus.(*ConsensusState).addVote(0xc424efd520, 0xc424e88780, 0x0, 0x0, 0x39, 0x1dc, 0x28c)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:1477 +0x1be5
github.com/tendermint/tendermint/consensus.(*ConsensusState).tryAddVote(0xc424efd520, 0xc424e88780, 0x0, 0x0, 0xd7fb00, 0xc42152ce00)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:1382 +0x93
github.com/tendermint/tendermint/consensus.(*ConsensusState).handleMsg(0xc424efd520, 0xcb58e0, 0xc42547feb8, 0x0, 0x0, 0x6, 0x0, 0x4, 0xed10ca07e, 0x3077bfea, ...)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:660 +0x9fc
github.com/tendermint/tendermint/consensus.(*ConsensusState).receiveRoutine(0xc424efd520, 0x0)
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:615 +0x5f5
created by github.com/tendermint/tendermint/consensus.(*ConsensusState).OnStart
	github.com/tendermint/tendermint/consensus/_test/_obj_test/state.go:332 +0x4a7
exit status 2
FAIL	github.com/tendermint/tendermint/consensus	76.644s
make: *** [test_integrations] Error 1
```

See https://github.com/tendermint/tendermint/pull/568

This fixes the problem with base-16 encoded values which may start with
digits: 015AB.... In such cases, the parser recognizes them as numbers
but fails to parse because of the follow-up characters (AB).

```
failed to parse tm.events.type=Tx AND hash=136E18F7E4C348B780CF873A0BF43922E5BAFA63:
parse error near digit (line 1 symbol 31 - line 1 symbol 32):
  "6"
```

So, from now on we should quote any values. This seems to be the way
Postgresql has chosen.

New pubsub package plus the query subpackage

test UnsubscribeAll properly
test BufferCapacity getter

> why we need it?

most of our subscribers will be RPC WS subscribers, so if there are too
many, nothing wrong with rejecting to subscribe.

however, consensus reactor must be the first to subscribe, since its
work depends on the pubsub package.

I've tried https://github.com/hashicorp/golang-lru/tree/master/simplelru today and here are
the results:

with LRU cache:

```
Benchmark10Clients-2                               50000             29021 ns/op         3976 B/op         105 allocs/op
Benchmark100Clients-2                               3000            363432 ns/op        36382 B/op        1005 allocs/op
Benchmark1000Clients-2                               500           2473752 ns/op       360500 B/op       10009 allocs/op
Benchmark10ClientsUsingTheSameQuery-2             300000              4059 ns/op          773 B/op          15 allocs/op
Benchmark100ClientsUsingTheSameQuery-2            500000              4360 ns/op          773 B/op          15 allocs/op
Benchmark1000ClientsUsingTheSameQuery-2           300000              4204 ns/op          773 B/op          15 allocs/op
```

without LRU cache:

```
Benchmark10Clients-2                      200000              5267 ns/op             616 B/op       25 allocs/op
Benchmark100Clients-2                      30000             42134 ns/op            2776 B/op      205 allocs/op
Benchmark1000Clients-2                      3000            552648 ns/op           24376 B/op     2005 allocs/op
Benchmark10ClientsOneQuery-2             1000000              2127 ns/op             462 B/op        9 allocs/op
Benchmark100ClientsOneQuery-2             500000              2353 ns/op             462 B/op        9 allocs/op
Benchmark1000ClientsOneQuery-2            500000              2339 ns/op             462 B/op        9 allocs/op
```

> How were you using the lru cache exactly?

I was adding a KV pair each time there is a match plus checking if
`lru.Contains(key)` before running the actual check (`q.Matches(tags)`).

```
key = fmt.Sprintf("%s/%v", query + tags)
```

query parser

use parser compiler to generate query parser

I used https://github.com/pointlander/peg which has a nice API and seems
to be the most popular Golang compiler parser using PEG on Github.

More about PEG:

- https://en.wikipedia.org/wiki/Parsing_expression_grammar
- https://github.com/PhilippeSigaud/Pegged/wiki/PEG-Basics
- https://github.com/PhilippeSigaud/Pegged/wiki/Grammar-Examples

rename

implement query match function

match function

uncomment test lines

add more test cases for query#Matches

fix int case

rename events to pubsub

add comment about cache

assertReceive helper to not block on receive in tests

fix bug with multiple conditions

uncomment benchmark

first results:

```
Benchmark10Clients-2                1000           1305493 ns/op         3957519 B/op     355 allocs/op
Benchmark100Clients-2                100          12278304 ns/op        39571751 B/op    3505 allocs/op
Benchmark1000Clients-2                10         124120909 ns/op        395714004 B/op   35005 allocs/op
```

124ms to publish message to 1000 clients. A lot.

use AST from query.peg.go

separate pubsub and query packages by using Query interface in pubsub

wrote docs and refactor code

updates from Frey's review

refactor type assertion to use type switch

cleanup during shutdown

subscriber should create output channel, not the server

overflow strategies, server buffer capacity

context as the first argument for Publish

log error

introduce Option type

update NewServer comment

move helpers into pubsub_test

increase assertReceive timeout

add query.MustParse

add more false tests for parser

add more false tests for query.Matches

parse numbers as int64 / float64

try our best to convert from other types

add number to panic output

add more comments

save commit

introduce client argument as first argument to Subscribe

> Why we do not specify buffer size on the output channel in Subscribe?

The choice of buffer size of N here depends on knowing the number of
messages server will receive and the number of messages downstream
subscribers will consume. This is fragile: if we publish an additional
message, or if one of the downstream subscribers reads any fewer
messages, we will again have blocked goroutines.

save commit

remove reference counting

fix test

test client resubscribe

test UnsubscribeAll

client options

[pubsub/query] fuzzy testing

do not print msg as it creates data race!

CLI Execute Error prints to stderr

common date parsing

v0.2.2

[log] tracing logger

[flowrate] refactor clock functions (Refs #16)

IsHex and StripHex

v0.2.1

copy log level parsing from tendemint