color() value function and wide color gamut notation

[dzuk-mutant]

I'd like to add support for wide colour gamut colour notation at some point, it's pretty widely supported now:

Information

• https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/color
• https://css-tricks.com/new-css-color-features-preview/

Some important things to pay attention to

• There are already some color gamut keywords (rec2020, p3, srgb) in Css.Media, so you might want to work out some sort of merge.