ColorFunctions: create constants for all of the functions as a sign of optimism
Color functions: implement rob, rgba, hsl, hsla, argb.

The implementation of ARGB uses a new node called Anonymous. I copied this approach from the less.js source.
Mixin test-case output tweaked to match now implemented rgba function
Color functions: more functions implemented

Hue & spin don't quite match the sample yet.
Color functions: use HSL functions from less.js

Still doesn't resolve hue not matching in functions-color.less -> .css. I have also tried another HSL->RGB->HSL converter and got the same result, so this example may not be correct. I will check to see how less.js handles it.
Color functions: implement saturation, lightness, red, green, blue, alpha, luma, mix, greyscale