#12 & #13 - Enable optional usage of Groovy CompilationConfiguration

This is in reference to Issue #12, and an extension upon Pull Request #13.

The pull request hadn't been updated in a while and it needed some cleanup before it could be accepted, so I took it upon myself to clean up the pull request. Here are my modifications:

1. Remove `mod/*` files accidentally commited.
1. Refafactor configuration creation into it's own method
1. Replace `try{} finally{}` with `withInputStream`
1. Configuration comes from java property instead of environment variable, since that's more in line with other vertx configuration.
1. If configuration property is not set, configuration may also come from a groovy script.
1. Added javadocs to class.
1. Updated tests

Eclipse CLA signed by `danny@kirchmeier.us`