Fix CSS number, percent and angle parsing

[RoBorg]

Should close #11

[WickyNilliams]

Thanks for this. Am I right in thinking that these formats are new to css colors level 4? I had not come across most of these! I'm struggling after a quick search to find any info online about browser support for these.

The hue value only supporting [0, 360] is a great catch, can't believe I missed that.

[RoBorg]

As far as I can tell they're all from level 3... looks like 4 introduces a load of new stuff that this won't parse :(

[RoBorg]

I used the docs here: https://developer.mozilla.org/en-US/docs/Web/CSS/color & https://developer.mozilla.org/en-US/docs/Web/CSS/color_value

[WickyNilliams]

I had a quick look through the v3 spec and it doesn't mention rad or turn units etc. I'll have a proper look at this next week and report back.