Support CSS Color Module Level 4

[ap]

The syntax now allows omitting the commas between values, in which case a slash must be used to separate the opacity value.

Lots of new functions added as well, for which sample code is provided at https://www.w3.org/TR/css-color-4/#color-conversion-code.

[figure002]

+1 Many modern linters expect you to use Level 4 syntax now.