Add support for Dart Sass

Created by: nex3

It looks like version 2.0.0 added support for Sass, which is rad! However, it also looks like it only supports Node Sass, which uses LibSass. It would be good to support Dart Sass, the new reference implementation that's distributed as pure JS, as well. This means that it doesn't require users to either download a binary blog or natively compile C++ code to use. See the sass-loader documentation for how to configure it to use Dart Sass.