Skeletal animation with basic physics

Skeletons are now FLxObjects and not FlxGroups. There's a few other minor changes but that's the big one. You can see the bounding box by toggling debug mode by pressing [~] then clicking the bounding box icon in the upper right.

Press [w] to jump, [a] or [d] to walk, hold [shift] to run, and [k] to kill yourself. There's not really anything to do here - just jump around and self-kill when bored.

Completed this time:

• Make sure skeletons play well with Flixel physics (collisions, velocity, acceleration, etc.)
• Detaching bones (exploding skeletons!)
• More animations for HumanoidSkeleton

Next up:

• Make sure regular sprites and animated sprites can be used as bones
• Constraints for joints
• Ragdoll physics