Accesskey / focus management additions

I added a link to the XHTML Access Module draft and extracted the important
requirements from that document into the wiki on access changes at [1].
Feel free to edit or flame me to the ground.

[1]
https://www.w3.org/WAI/PF/HTML/wiki/Accesskey#Implicit_Use_Cases_from_XHTML_Access_Module

-- 
Shane McCarron
Managing Director, Applied Testing and Technology, Inc.