First pass at ua-parser filter.

This filter integrates the user_agent_parser gem to allow parsing
of User-Agent strings in to structured data. This can be used for
real-time analytics or other interesting things from your web server
logs.
Allow updating the regexes.yaml out of band.

Add configuration to allow using a regexes.yaml other than the
one shipped in user_agent_parser. Updated files can be found at
https://github.com/tobie/ua-parser
Fix typo on logger line.
Incorporate uaparser feedback, make flatjar work.

* Handle running inside a flatjar. (technique taken from geoip filter)
* Rename field/container to source/target
* Allow target to be an existing hash in which case data is merged
* Better comments
* Allow arrays for input (though only parse the first element)
* s/'/"/ and add parens to function calles
* Changelog entry
Merge pull request #347 from wotifgroup/ua-parser

Add HTTP User-Agent Parsing Filter