Added basic drawing example, using graphics
Updated skeleton.rkt, now draws avatar and obstacles

- using code from https://github.com/LnL7/racket-canvas-example-1
Updated skeleton.rkt, now animates and has gravity

- changed PhysicsEngine.update-time!, to adjust game speed

Conflicts:
	canvas.rkt
Updated skeleton.rkt, now has keyboard input
added lang definition for skeleton.rkt
Added basic example using objective.rkt
renamed skeleton.rkt