Font Tweaks
#CHANGE: Improved text rendering performance (EmitVertices)
#CHANGE: Removed variable glyph coloring from Font class and steamlined bitmap generation.
#CHANGE: Font Bitmaps are internally no longer RGBA textures, but Alpha textures instead.
#CHANGE: No longer using DrawTechnique.Invert as error technique. Now using DrawTechnique.Solid instead.
#ADD: Added some static by-ref methods to ColorRgba for arithmetic operations.