freetype.c: Revived and revamped old yuva renderer

Highlights:
  Three rendering modes: Outline, Fat outline and background
  Better looking
Drawbacks:
  White only at the moment
  no yuva blend filter for some chromas
  
the old renderer is available with the --freetype-yuvp option, since this is
needed at least for dvbsubs encoding. (and for people with no usable blend
filter)