add Groovy support, copying Java syntax

[neontapir]

I've done basic testing of this against my own repositories.

[adam-waldenberg]

@neontapir Thank you.

I looked at the syntax, and yes, it seems using the regexps defined for c/java should work just fine. Will merge this once I have some time.

[neontapir]

I apologize for all the Git chatter. I wanted to submit a separate pull request to address an issue I found with specifying extension filters. My master branch now only contains those Groovy additions.