Non-blocking CSS loading

By default CSS files loaded through LINK tags are downloaded synchronous, while an asynchronous approach would be preferred. 

By setting the media attribute of the link tag to a non-matching item the browser will treat it as non-blocking, making the request async. Once the CSS has been loaded the media attribute is reset to `all` so it will match and the CSS will get applied.

This is based on information found at: https://gist.github.com/scottjehl/87176715419617ae6994