Improving mapping of JBoss log levels

Hi, we're using your gelf module to connect our JBoss AS 7 to a graylog server. Since we had some issues with the log levels (ERROR was treated as DEBUG etc.), we decided to add some log-level matching that supports the JBoss log levels. In case you are interested in those changes, here's the pull request.

(sorry, I also did some re-formatting... I know that doesn't make it easier to read the diff but I don't have time to change it now...)

Cheers!
Nils