Rolling back to before I started the delayed-evaluation stuff. Didn't checkout an older commit because I wanted to keep some of the new stuff.

Parsing mixin definitions, and tweaking the other functions to handle one-pass parsing and expansion.

Handling hex arithmetic. Ignoring more janky edge cases. Probably need to handle decimal rgb formats too.

New node type for hex triples. Modified the emitter to print hex triples correctly. Next: hex triple arithmetic.

Handling arithmetic with units. Gonna' forget about janky edge cases for now -- people shouldn't be doing arithmetic on lists anyway.

Expression evaluator is mostly working. Still need to correctly handle multiplying and dividing with measurement units. Also need to correctly handle hex arithmetic. Finally, need to see if I can't handle more weird edge cases.

Working on evaluating arithmetic expressions. Tough because of Sass's liberalism and the fact that '/' can be both a division operator and number separator.

Parsing complete list and expression syntax (I think). We'll know for sure when it actually gets emitted.

Properly handling arbitrarily complicated args to :not. LET THIS BE THE END OF SELECTOR PARSING (until interpolation).

Holy crap, the new lookahead functions are working. The parser essentially does backtracking now. May be worth it to characterize selectors with a massive regexp and do lookahead that way.

Properly emitting back-references. This should conclude selector parsing and emission until we're ready to tackle interpolation.