chore(build): Adding Sass to Grunt pipeline

Adding Sass and Autoprefixer into the mix. This also means we need a dist/ directory, so things are about to get "weird".

Took a rough stab at documenting the available Grunt tasks, although some are subject to change once we get minification and other things involved.
thanks for the README cleanup. would be cool to put into a separate commit in general, but not a big deal at this early stage