Create SPLITPEAK-styleguide.md

This is the styleguide to be followed when writing any style code for splitpeak's website or any of its clients. Pretty much anything intelligently written or any cool ideas were completely ripped off from Medium.com's styleguide.

Here's a blog post about it. It's a good read if you're sick of writing CSS like it's 2001 or you're sick of trying to use _every single language feature of LESS_