Platform graphics + collision basics

2014/03/14

-Added preliminary background graphics
-Mostly platforms at an oblique angle - will probably need a couple more
tiles for other cases.
-Decided against having a collision box for player that is smaller than
character graphics
-This would only really be useful if there were enemies
-Jumping now has two conditions:
-If the player has a yVel which makes the player appear stationary
-If the player is touching an object
-This may cause problems when the player is touching the ceiling
-Added some basic collision detection for when the player collides with
a single object