Shared lua code

I've added ERB templating support to the code base. This would allow a user to share lua code between multiple scripts. I'd written a handful of scripts today that had common code elements between them and wanted to reduce duplication to avoid maintenance headache.

I've added corresponding documentation and written an adequate MiniTest test case for the feature. I'm not very familiar with that test suite in particular, so the test could definitely be more awesome.

Thanks for making my life easier with Wolverine!