implement hitboxes and collision detection

[noah1510]

Since collision detection is essential for any game engine, there should be a least a simple implementation when this is public.

[noah1510]

In combination with #39 a detected collision should trigger an collision event which can be caught and handled as the developer needs to.

Collision should be checked for each actor (#38 ) not game_object ( at least for now), allowing backgrounds that cannot collide at all, or at least unless the developer decides to write a custom check for those objects.
Collision will be checked for every game_object.
There should also be a property that disables collision for a subclass of an actor game_object or an specific instance.