Grok documentation updates

* Added mention of grok data type conversions
* Minor docs cleanup
Merge pull request #313 from jamtur01/extendocs

Minor additions to the extending documentation
Merge pull request #326 from vbatts/PHONY-jar

Makefile: make the monolithic jar PHONY, so it builds everytime for the jar target
Merge pull request #325 from vbatts/LOGSTASH-734

Work around JRUBY-7052 (LOGSTASH-734) fixing the geoip database embedded in the jar.
Merge pull request #327 from jamtur01/grokdoc

Grok documentation updates
Allow configuration of whether the grok filter tags events on failure
Update contributors
Include changelog entry
Merge pull request #328 from neilprosser/master

Allow us to configure whether the grok filter tags on failure
- don't include backtraces
- reduce date perf test requirements for now since they're failling
  intermittently on jenkins.
- jrubyc target java 5 again (since without it, and compiled under jdk7,
  you get jdk7-only class files)
Added : as a valid separator between seconds and subseconds
Merge pull request #331 from blewa/master

Added : as a subsecond separator.
Fix '@tags' not in log4j input
Copy amqp output plugin into rabbitmq file
Change AMQP to RabbitMQ names
Remove 'name' field
Remove amqp output plugin
Rename amqp input plugin to rabbitmq