Allow custom importers.

[jgerigmeyer]

Fixes #24.

If a user passes in a custom importer option, this PR now passes that option through to node-sass. It also modifies the sass-extract specific importer to preprocess the filepath through any custom importers first.

node-sass accepts both sync and async versions of importer fns, and also accepts an array of fns or a single fn. This PR supports (and tests) all of those cases.

If the user, however, has an importer fn which returns { contents: <...> } (instead of { file: <...> }), that is not supported. It will still pass through to node-sass (so the files can be compiled properly), but sass-extract won't be able to extract variables from those imports. I think those would be unusable by sass-extract in any case?

[jgerigmeyer]

Updated the PR to support custom importers which may return absolute import paths.

[jgerigmeyer]

@jgranstrom Any thoughts on this?

[jgranstrom]

@jgerigmeyer thank you for this, and sorry for the late reply. There should definitely be support for providing custom importers, so this is great.

I will merge this and include it in a new release, however before that it would be great if you can amend the commit messages and change the message format to the convention used in all other commits and mentioned in the readme to keep it consistent and generate changelogs. There is some details on that process available.

[jgerigmeyer]

@jgranstrom Rebased with new commit message. Let me know if that looks okay!

[jgranstrom]

@jgerigmeyer perfect, thank you! I’m currently a bit off the grid but will try to release this later today!

[jgranstrom]

I published this in version 2.1.0. Thank you for the contribution. Make sure to get back to me if you find any other features missing for your use cases.

[jgerigmeyer]

Thanks!