Replace set_mass, with set_mass_sphere and set_mass_box
Change responsive_body() to body()
Rename physics_engine() to physics() and make it return a reference instead of a pointer
Change collidable() to shape()
Undo over greedy renaming!
Finally trackdown and fix the weird disappearing objects bug
Make it easier to create cubes and spheres
Switch Light& to ProtectedPtr<Light>
Merge remote-tracking branch 'upstream/master'