Finally fixed rendering.  Hacked in Renderable as a glue component for communicating position from GOs to the renderer.  Next up: input and control.
Got the basic input figured out.  Pre-unit conversion commit
Unit conversion is fully implemented.  1 unit is the equivalent of 1 map tile.
Beginning implementation of collision detection.  Fixed up collision.py, and refactored Tiles to inherit from GameObjects to simplify collision algorithms.