Docs: clarify how multiple values work for various options

[akx]

I spent a long while wondering why comma-separated values wouldn't work for CIBW_SKIP, since this information was cleverly hidden inside the Examples box:

This PR unifies that for all of the multiple-values-supported options; this was already documented in the prose for the environment variable options, so the extra repetition of the same information is now gone from the example box's footer.

[joerick]

I believe we put them in the tabbed box because that rule only applies to environment variables. In TOML, the options are supplied as a list of strings.

[henryiii]

Maybe we could improve the error message?

[akx]

I believe we put them in the tabbed box because that rule only applies to environment variables.

I could edit this to mention that in the prose.

Maybe we could improve the error message?

There is no error message – in the case of a malformed SKIP, cibuildwheel just tries to build everything since a pattern like pp*,foo matches nothing (and in the case of my project, failed on PyPy because I use CPython-specific APIs).

It would maybe better to "Do What I Mean", i.e. allow e.g. a [,\s]+ regexp as a separator?

[henryiii]

cp31{2,3} is a valid expression.