Add State to underlying Repl monad.
Have the evaluator use the Repl/State monad.

Also skip lines that are all whitespace.
Switch from Maps to Tries for environment.
Add bound var autocompletion on <TAB>.
Don't complete when inside a String/Char literal.
Merge branch 'dev' of github.com:evancz/elm-repl into completion

Conflicts:
	Repl.hs
Fix bug in `:flag remove ` in handleCommand.
Merge pull request #23 from maxsnew/completion

Basic Autocompletion