Tile collisions

Fix #1884. This is an inprogress shot of replacing the collision detection with precise detection. The following levels have been adjusted

- Town (ignore the weird blocks and ramps)
- Valley Sandpits 2
- Valley 2

What I need from everyone else is testing. Pull down the branch and test. You'll need to jump straight to those levels I listed above (otherwise it will crash).

@edisonout I'm really looking for you to test, since you've had trouble with our slopes before. 

Also note, enemies and nodes and a bunch of other stuff is broken as well.