System: Add AVR code
Main: Replace time() with GetTicks()
Remove old SDL includes from cBlock and cSquare
Screen: Stub out SDL code on AVR
Use square top left instead of center for collisions
Updated location of next piece circle
Change some locations to grid coordinates

Instead of pixel coordinates.  This makes tilemap-based rendering easier.
Add a blank square enum and tile
Add image/palette/tileset data headers
Screen: Add AVR/ChronoCube rendering code.
Screen: Enable color cycling for AVR