Alias PixelFormat.nv21

Instantiates indexed dsdl2.PixelFormat for use with dsdl2.Palettes from SDL_PIXELFORMAT_* enumeration constants (from SDL 2.0.4)

class PixelFormat
{
  // ...
  alias nv21 = _instantiateIndexed!(SDL_PIXELFORMAT_NV21,0,4);
  // ...
}