Pages: Upgade guide to QUnit 2.x

Fixes #86 

First draft for an upgrade guide. There are no links to this page, yet. There are layout issues, may need to port some CSS from jqueryui.com.

Would be good to get some feedback on the format. Also, am I missing something?
Nevermind, I read the later comments. I'll get rid of the Overview section and merge it into later sections.