Switch from using jeromq to jzmq.
Added a new ZMQLogbackAppender.

This is a fork of ZMQAppender, but for logback rather than log4j.

This includes some simple changes to LocationInfoData and LoggingEventData
so that they can cope with data from either source.
Pass an empty array if tags == null.

Logstash 1.1.6 doesn't parse the event if @tags=null.