fix in indexing for maximal coordinates (unused by default, still experimental, requires many iterations for Minitaur due to extreme mass-ratio, hence use of reduces/generalized coordinates)
modify quadruped.py to test maximal coordinates
wrap angular servo (positional) target within [-PI,PI] in btGeneric6DofSpring2Constraint
add 'j' key to show body frames in wireframe/debug mode
added test urdf files for minitaur with all fixed joints, or fixed knees.
added some stiffness/damping to minitaur legs (testing)
tiny_obj_loader, don't crash on invalid texture coordinates
btMultiBodyConstraintSolver: sweep back and forward to reduce asymmetry
add minitaur quadruped playback of minitaur log files (real robot and simulated create the same log files)
add improved minitaur.urdf file, see https://youtu.be/lv7lybtOzeo for a preview.
