Updated sprites
Copied over improvements made on the animatron-game-center repo. This repository is free-standing, but has a structure that allows it to easily be placed into the game center when needed.
Bugfixes, collisions, and sprites

Fixed a bug where going outside of the road boundries caused the car to
stop. Fixed the car sprites, so it no longer looks like it's popping a
wheelie up hills.
Added crashing. when the car crashes into an object, it explodes for a
time relative to it's percentage of max speed. If you crash into another
car, your car is slowed significantly relative to your's and the other
car's speed.
Accounting for centrifugal force in turns
New gitignore
Merge branch 'master' into develop