Add LibratoWriter

Port of LibratoWriter from embedded-jmxtrans project
Add javadoc
Simplify method
Remove debugging output
Remove debugging output
Merge pull request #141 from farnulfo/add-librato-writer

Add librato writer
Writer for Log4J
Put the parameter to allow dot keys in the JSON configuration level. It's query specific as the keys specifications are.
This commit includes the modifications of rmarmier (regexp) and the correction for the tab character.
Merge pull request #146 from Cousnouf/master

Put the parameter to allow dot keys in the JSON configuration level.
Merge pull request #144 from YannickRobin/log4j

Writer for Log4J
upgrade some versions
fix build for log4jwriter