Added a begin contact method and an end contact method. Turned
collidable into an Abstract class so that not all methods are required
to be implemented.
Merge branch 'master' of git@github.com:PunchlineGames/JavaLib.git
[IMPORTANT] @Natman64 @GenericCode ONCOLLIDE renamed to onContactBegin.
Added onContactBegin and onContactEnd methods. Collidables changed to
abstract classes. Implementation of all methods no longer necessary
(default continueCollision returns 1). Code refactored for all games
created (including NinjaSpacePirate).