Initial implementation of rect.

This includes a basic Rect object, and a function to turn rects
and rect-like tuples into SDL_Rects.

We still need to implement the dozens of properties and functions
that the real rect object has.
Initial implementation color.

Right now, just a function that turns an RGBA tuple into a pixel
value.
Add Surface.fill()
Add get_init, get_surface, and update.
Update setup and test to match the newest code.