Update README
Fix quotes in script
Add icon
Make build defaults sane
Port to OpenGL 3.2 core profile

This makes the game functional on OS X.
Fix compilation errors with GCC
Add support for both GLSL 1.30 and 1.40

Mesa is only up to OpenGL 3.0, and OS X offers either an OpenGL 2.1
legacy profile or an OpenGL >= 3.2 core profile.  So, while we need at
least GLSL 1.30 in order to get the "flat" qualifier, we need to provide
GLSL 1.40 shaders in order to run on OS X.
Fix icon and app category on OS X
Change default resolution to 1080p
Fix Visual Studio compilation issues
Update README