Merge pull request #5 from zacharyw/master

Added a start menu
Removed extraneous game files.
Add spawner to board.
Implement spawn logic.
Change fill type for spawner.
Merge pull request #6 from ccallebs/feature/add-spawner

Add Enemy Spawner
Enemy removal bug

Fixed the bug where enemies would be randomly removed. Also made
collision detection slightly more performant.