Add Option to Disable Antialiasing

An option to disable anti-aliasing would expand usefulness for specialized situations.

Example of usecase that is broken by AA: I've been working on a project that involves stroking paths with a series of circles that change color based on distance from the start of the path. I can then use a specialized shader in a raster pipeline to threshold the image, giving a hand-drawn line that can be 'drawn' in real time with extremely light loads on both CPU and GPU. To do this, I need every pixel of a circle to be either 100% the desired color or entirely transparent. Anything inbetween results in artifacts.

My current workflow involves copying paths out of an SVG into a python script to generate these stroked textures, but Graphite provides a very enticing alternative.