* Add a debug view that draws the player bounding boxes.
* Improve the collision detection to add support for:
* Doodads being "Grounded" so gravity need not apply.
* Walking up hills, albeit a bit "bouncily"
* Harder to clip out of bounds
Known bugs:
* The Pixel format in the Grid has DX and DY attributes and
it wreaks havoc on collision detection in Play Mode when you
come straight from the editor. Reloading the map from disk to
play is OK cuz it lacks these attrs.
