Make bodies non-transparent by default.
Fix up package naming confusion for the moment.
Fix up settle-to-markers.
Try to improve rendering performance by scheduling draw events manually. (Pyglet over-schedules draw events by default.) Add a function for saving rendered frames to disk. Change the size and color of the floor checkerboard.
Remove object-tracing methods -- clients will probably want to implement their own tracers and can hook into the step() method of the World class.