Add auto to the boundary output.
Add auto to the boundary output.

This will pull fields from @fields and put them in the request to
boundary. I attempted to make it backwards compatable but I don't see
any way to test that.

feature/boundary-auto

joekiller/logstash-kafka,tinglinux/logstash-kafka,Aloomaio/logstash-kafka,tinglinux/logstash-kafka,joekiller/logstash-kafka,Aloomaio/logstash-kafka,opentable/logstash-kafka,opentable/logstash-kafka