Support file globbing for @imports

[jcsmorais]

See https://github.com/less/less.js/issues/1181 for additional details, such feature has been implemented on node side by https://github.com/just-boris/less-plugin-glob, it would be super useful to have it available within less.php too.

E.g.:

@import "mixins/*.less";
@import "components/**/*.less";