Group numbering

This branch includes the last-minute changes made for the demo last week, detailed below:

* Adds a group for the entire match (on par with other regular expression libraries)
* Fixes a bug in split that caused the first element of the resulting array to be dropped.
* Renames the UncompiledRegexp class to Regexp for brevity and to avoid confusion.

*Note: I'm merging this now due to time constraints*