Asynchronous loading section should add fully non-blocking

[bluesmoon]

Scripts that can be loaded asynchronously but still block the onload event should receive a B rating. Only scripts that can either be loaded in/after the onload event or scripts that use the advanced Iframe Loader Technique should get an A rating.

The loader is described here: http://calendar.perfplanet.com/2012/the-non-blocking-script-loader-pattern/