Create a library for continuous 2D collision

[kstrafe]

We currently have tile-based continuous collision. We should attempt implementing arbitrary coordinate 2D continuous collision.

• [x] Implement the boolean GJK algorithm in 3D
• [ ] Implement spatial partitioning (BSP, quadtree, or octree?... AABB?)
• [ ] Create an interface
• [ ] Pack it as a library

We can implement continuous 2D collision by extending points on 3D as (old_x, old_y, 0) -> (new_x, new_y, 1).
Can spatial partitioning exploit this in some way?

[kstrafe]

I think a simple function will suffice (just calling the GJK algorithm). We'll figure it out later.