add (very basic) sass to _s

We here at WebDevStudios love _s, but one of us always has to "Sassify" it. I wanted to share our basic setup, in hopes that others find it helpful - or maybe encourage some folks to give Sass a try.

I kept it basic by splitting up each section into partials, added a few variables, and one REM mixin. Would love others to pitch in and expand!

Note: I did not include style.css, since after being compiled, it changes the indentation.