Language definition for Groovy

This is a language definition for [Groovy](http://groovy.codehaus.org/). I've put up a page that executes a set of Jasmine tests against various examples of the syntax [here](http://freeside.co/prism-groovy).

As discussed in #88 I can simplify the *wrap* hook a little once the language is passed to the callback but this is a working implementation that doesn't need it.