13 ENHANCEMENTS: * Added palettes to set density, bouciness, and friction (w/Sai Vineet) * Added palette to set motor speed, rotation (w/Sai Vineet) * Added chain tool (w/Sai Vineet) BUG FIX: * Updated Box2d version to eliminate some memory leaks (Sai Vineet) 12 ENHANCEMENTS: * Added option to joints to set collideConnected = False * Added clear_all (Sai Vineet) * Added tracking (Sai Vineet) * Added tracing (Sai Vineet) * Added erase traces (Sai Vineet) * Added save/restore of pens and traces (Sai Vineet) BUG FIXES: * Removed cjson dependency for elements * pep8 cleanup (Sai Vineet)