Merge pull request #78 from bvssvni/master

Added support for RGB images
Merge pull request #82 from bvssvni/master

Renamed `XYRGBA` to `XY`
Merge pull request #83 from bvssvni/master

Using better name on shaders
Merge pull request #85 from bvssvni/master

Moved in `glyph_cache` from Conrod
Added `draw` method

Closes https://github.com/PistonDevelopers/opengl_graphics/issues/81