Started work on subpixel rendering.

Subpixel layout is currently hardcoded as RGB, but it should be setable
from commandline in the future as a smoothing parameter.

Values for this upcoming parameter:
mono - No pixel smoothing at all.
gray - (previous rendering), non-subpixel smoothing
rgb - Subpixel smoothing with RGB horizontal order
bgr - Subpixel smoothing with BGR horizontal order
vrgb - Subpixel smoothing with RGB vertical order
vbgr - Subpixel smoothing with BGR vertical order