Added folder and file to implement the Iteratee SM.
Renamed to enumerator, since we'll be using that library.
Added main loop and basic plumbing.

I've added the "main loop" relying on an enumerator which transforms
the strings to actions and emits them to the iteratee. There is a
credit iteratee, but it's quite dummy yet.
Credits are modified by 'Play' and 'Coin'.
Now, cannot execute 'play' while not enough credits.
Added a minimal version of the GameState.
Merge pull request #79 from jeslg/slot-iteratee

Slot iteratee