Collision detection system

[aostrega]

This is related to standard gameplay types (#40).

Design and build a modular system for collision detection that is flexible enough to reproduce the collision handling of everyone's favorite games.

A game object's collision detection is often split into a broad and a narrow phase - one to find potentially colliding game objects, the other to get the state of collision with a specific game object.

A broad phase is optional and can involve a quadtree, a tilemap, AABB testing....

There are various narrow phase types and range roughly from adjacent square tile checking to testing moving bodies with arbitrary shape and mass.

Collision detection & handling for a game object can happen before or after its position is updated in a frame.