Todo:
- Add version(StdDoc) sections that document the getter/setter functions, as they're not really visible with the current mixins.
- Add some missing documentation from the C sources and fix them so they match D semantics.
- Add documentation building (probably through DUB).
- See the Box2D test-suite and port some of the interesting samples to our test-suite.
- Implement the DRAW_GJK debug drawing routines.