Finished documentation

Finished documentation on sprite physics and joints
Fixed some bugs in sprite physics
Added safety checks for joint types
Added code to free up joints when a canvas is destroyed

rcbasic_runtime/rc_sprite2D.h

@@ -78,6 +78,8 @@ struct rc_b2Joint_obj
 
 	int type;
 	bool active;
+
+	int canvas;
 };
 
 irr::core::array<rc_b2Joint_obj> rc_joint;