Good day!

I wanted to use the resolve option in order to resolve files from the compose: import. Unfortunately this option only gives me the possibility to resolve the "first layer" of composes.

Consider the following setup:

// a.css
.a {
  composes: b from "./b.css";
}

// b.css
.b {
  composes: c from "./c.css";
}

// c.css
.c {
  content: 'c';
}

In this setup the a.css file is my entry point. The resolve function will only be fired for the composes: b from "./b.css" statement. The "deeper" import inside b.css is completely opaque.

For this usecase I've implemented the fileResolve option in a non-breaking manner. This function will be called for all composes statements no matter how deep they are.

• It receives two arguments file and importer, both of which are strings. The file is essentially the part between the brackets after the from keyword (same as the first argument of the resolve option). The importer is the file from which this compose statements comes from.
• It has to return string | null or a Promise<string | null>. The returned string has to be an absolute path. If null is returned the default resultion takes place.

I haven't done that, but with this change I would propose to deprecate the current resolve option, because the new fileResolve
option is a bit more powerful, still straight forward to use and can still do the same thing as the resolve function.

The README would also need an update, but I would do that after I the feedback from this PR.

Fixes: #131