Add a basic REPL, and a Makefile
Parse () -> Unit
Add check target to the Makefile
s/Env/Rusp/, move rusp::parse::parse to rusp::parse; .gitignore & Makefile modifications.

(The parse module has to become parser for the parse movement to work.)
Merge pull request #2 from huonw/repl

REPL! (Huon Wilson is awesome)