Adding shadows and ritual

Refactored sprite and gameobject code a bit
Added darkness - a big image that shrinks to "encroach" on the player
Added ritual - run in X number of circles to perform it.
Added constants file - gives designer access to tweaking numbers (e.g.
number of circles in a ritual)
Added timer functionality (though it could use some refactoring before
being used for animation)
Fixing a bug in ritual code

Ritual code was hitting a race condition - if you hit a new button
before releasing the old one in the wrong order, it wouldn't register
your circle. Should be fixed now.