Add compress layout

As an answer to drawbacks of Liquid in your [article about Jekyll](http://homes.cs.washington.edu/~asampson/blog/jekyll.html):

> No whitespace control. This means that every {% if %} and {% for %} you use craps up your HTML output with ugly spaces and newlines.

I propose to compress whitespace with my [layout](https://github.com/penibelst/jekyll-compress-html).