Box2d integration

Chipmunk2d has been implemented in Play.date. It requires a bit of fiddling around to get it going, and I could only get it building under a Linux box, rather than Windows (due to requiring an ARM cross compilation, and issues with my Windows environment, ymmv).

See this older forum post: Chipmunk2D Physics demo

I'm messing around with trying to create a simple Pinball machine for the Play.date, starting with the sample code from that demo. The hardware seems capable of running 6 to 20 objects, although I'm only using spheres and static polygon bodies.