Merge pull request #1 from dgym/master

Added antialiased dice rendering.
Merge remote-tracking branch 'dgym/master'
Shader code lives in its own module
Fixed FBO rendering problem caused by gl_FragCoord

gl_FragCoord is relative to the frame buffer's origin,
which Kivy gives no way of determining. Switched to
using a variable set up by a vertex shader.
Fixed blending artifacts while rendering dots.

This caused a black outline when rendering on the
new red dice background.