Add new return values

This PR

- Uses a standard gem structure as defined in http://guides.rubygems.org/gems-with-extensions/
- Adds rake-compiler to compile the gem
- Adds a useful `rake console` shortcut for jumping into an irb console.
- Adds some basic tests covering what values and types should come back.
- Ensures strings are marked as UTF8 before passing them back to ruby.
- Adds new return values (see 4adabfa)