Each bundle of four pixels on a scanline is packed into the RGBA channels of
the mask texture. The area LUT is also expanded to be RGBA so that four pixels'
worth of areas can be looked up at once.
Nice improvement on `paris-30k` from MPVG.
Closes#262.
distance-to-edge for stencil analytic antialiasing.
This improves the rendering quality of stencil AAA significantly.
Additionally, this adds an approximation of Core Graphics' (macOS')
defringing filter.
Closes#73.
Patrick Walton