[dogstatsd] Add dogstatsd output writer

This is a new OutputWriter for DogStatsD which includes basic tag support. It's a copy paste of the `StatsDWriter`, with the patches from https://github.com/jmxtrans/jmxtrans/pull/77 and the proprietary tags as used by [java-dogstatsd-client](https://github.com/indeedeng/java-dogstatsd-client/blob/master/src/main/java/com/timgroup/statsd/NonBlockingStatsDClient.java#L216).

Still to do:
* test to see if this even works

/to @alexism