Compatibility with PostCSS 8

[jonnitto]

Currently, this plugin is not compatible with PostCSS 8, also because postcss-import is not compatible yet. It would be great if you could make these plugins compatible with the latest version.

[bcomnes]

Here is a link to the migration guide:

Looks easy to get things moved over preliminarily but I (just a user) unfortunately don't have time atm. Low hanging fruit for anyone else though:

https://evilmartians.com/chronicles/postcss-8-plugin-migration

[niksy]

Easiest way is to transfer everything to Once method. Do we want that or should we use more performant API? There’s only one walker defined (for declarations), and running tests on that walker produces some errors.