Add Functions

[Elchi3]

I've used compute_from to ignore some late-additions which are also all baseline high already.

[autonome]

Re filename - it opens the prefixing question, eg JS vs CSS functions. If we don't prefix one, we'll have to prefix the other, so in that case maybe should prefix both?

[ddbeck]

Overall I like this! I kept trying to nit pick some of the compat keys and then convincing myself you had it right. Nice work! Just a little wordsmithing to do here.

[ddbeck]

If we don't prefix one, we'll have to prefix the other, so in that case maybe should prefix both?

@autonome I'm not sure this will be a problem. CSS doesn't (yet 😬) have custom functions (and it'll probably be known as "custom functions" if/when it does), only predefined functions that slot into neat groups (e.g., transforms).

[Elchi3]

Should we merge this?

[ddbeck]

Yes, let's merge. Patrick, if you have more suggestions for the description, please open a follow-up PR. Cheers!