More physics and graphics pipeline updates

Added fullscreen and pausing (pausing doesn't work because it toggles
every update if the esc button is pressed). Added some rendering
structure and put in place some physics methods.

The Polygon class is designed for speed. It holds a lot of data about
itself instead of calculating it every time physics need to be
calculated. It will probably hold more data in the future. Still looking
at ways to do collision detection for polygons.