New Graphite Codec

This codec will soon replace the need for a graphite input and output.
The tcp inputs/outputs can be used in conjunction with the graphite codec.
This lets us consolidate the many different ways various tcp based plugins
handle timeouts, exceptions, etc.
Graphite Codec Tests

I added more tests the the graphite codec to cover
instances when various parameters are set. I choose
not to write tests for inlcude/exclude_metrics
because the default value is used when encoding.
Add graphite codec to CHANGELOG
Fix travis builds
Merge git://github.com/logstash/logstash