Logback Layout class that can produce GELF messages

We are not currently using graylog, but we are wanting to start processing our logs in Hadoop.  We wanted to make our logs parseable and found GELF in our research.  We may be integrating graylog in the future, but we wanted to make the change to parseable logs now.  So we need to produce GELF format in a way that can go out into any Appender.  I simply created an implementation of Layout that uses your GELFConverter class to create the GELF message.