Pig support (2nd attempt)

[2nd attempt because I corrupted the git branch for pull request #224]
I added support for using the ua-parser in pig.
This allows using the ua-parser library for doing clickstream analysis on a Hadoop cluster.

Implementation overview:

Some cleanups and additional safety checks in the java library
Additional CachingParser (java) to avoid needless CPU usage when parsing the same UA again and agian.
Separate pig client that depends on the java version of the library.