Less color functions don't work with css variables

[badlydrawnrob]

For now, in general, I'm using as little functionality from Less CSS as possible:

• [x] CSS nesting (which is now included in the CSS spec on modern browsers!)
• [x] @import for including css partial files (very helpful to keep a sane structure)
• [x] #37 and I don't care!

And that's about it. So avoid Possibly best to avoid fancy but ultimately wasteful features — colour functions area nice-to-have, not a need-to-have. Nor do they work nicely with --css-variables anyway.

Keep it simple, stupid!

[badlydrawnrob]

I don't care because I'm not going to use them. CSS nesting will be the default anyway.