DevGuide: Add Eve Output Plugins
Eve output plugins work pretty well in 6.0 and git master but need to be documented. Now that I think we have the API good for 7.0 we can documentat it as only minor (if any) changes will likely be made before final release.
An example plugin covering all the details exists at: https://github.com/jasonish/suricata-example-plugins/tree/master/eve-filetype
The guide should be more about the API (registration functions and API) then about how to build and install plugins which should probably be in the user guide and not covered here.