added support to set a message format
added support to set a message format

this is basically the same support for formatting the payload as in
the stdout output

i use it for a quick hack to post to a collector of cube
square.github.com/cube

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