Invoke new thread to avoid 'mutex can't lock' issue
fix to accept comments for json literals
parser.rb: Make ':' optional after pid

In some cases, there is no ':' after the pid, the following log would fail to parse

```
<77>Jul 11 15:14:01 my.example.com run-parts(/etc/cron.daily)[8231] finished logrotate
```

resulting in

```
"_source": {
    "data": "<77>Jul 11 15:14:01 my.example.com run-parts(/etc/cron.daily)[8231] finished logrotate",
    "message": "invalid syslog message data=\"<77>Jul 11 15:14:01 my.example.com run-parts(/etc/cron.daily)[8231] finished logrotate\"",
    "@timestamp": "2014-07-11T19:14:01+00:00"
  },
```

This PR aims to make those ':' after the pid optional
Merge pull request #380 from fluent/fix-multi-process-stop-on-ruby2.1

Invoke new thread to avoid 'mutex can't lock' issue
Merge pull request #382 from Mylezeem/make_column_optional

parser.rb: Make ':' optional after pid
Refactor SyslogParser test
Merge pull request #383 from tagomoris/v1config_literal_with_comment

fix to accept comments for json literals
Use NULL  before @log.init called
v0.10.52
Use an Integer instead of an Array for error count.

Using array for error count consumes lots of memory when
retry_limit is large. We don't use an item in @error_history,
so we can use simply number count instead of array based approach.
Merge pull request #386 from fluent/use-num-count-for-retry-count

Use an Integer instead of an Array for error count.
Add flush_multiline_interval and flush_multiline_wait option to NewTailInput