Tweak PLAYER_SPEED
Initial refactor into states

Refactor all of the existing code into a BlockToBlock.Game state

Use the StateManager to switch to the state.

Remove incorrect world.destroy() code now that states are used.
FIXME: some keyboard input callbacks don't seem to be cleaned up.

Possibly broke things
Merge branch 'master' into gh-pages

* master:
  Initial refactor into states
  Tweak PLAYER_SPEED