Add `pcss` and `sss` file extensions
Add `pcss` and `sss` file extensions

Why we need `pcss`: We don't,  but a lot of users are familiar with the `pcss` file extension convention for PostCSS.
Why we need `sss`: The [SugarSS](https://github.com/postcss/sugarss) syntax has a [syntax highlight plugin](https://atom.io/packages/language-postcss-sugarss) that only recognizes this extension...
jenius/accord