Add scss version.

Hey Adam, saw you were looking to add a scss version. There’s not much work here other than copying the `.less` file and changing the variable syntax.

Here’s a compiled gist version for you to check over - http://sassmeister.com/gist/benjaminparry/8b771dc13770d0858f60

I’ve added to the `dev` directory as stated in the readme, hope I’ve understood that correctly.