Moved to sdl2

Some cleanup done, working on adding some interactive controls to the gl board so I can set up games and step through with the "AI".

Preliminary AI work is underway.  The idea is that the AI can look several moves ahead and try to work towards captures, however I haven't encoded jumping correctly, so even that limited AI is not working.
Fixed SDL2/openGL bugs

gl_checkers is now working on the laptop.
The "play" button has been added, but isn't doing anything yet.
Fixed checker board, working look-ahead AI

Checker board squares were backwards; black is now in the bottom left corner like it's supposed to be.
AI looks ahead for to captures, it picks the move that can lead to the most captures for the given color and least for the opponent.