[XHR] responseType "json"

[Anne van Kesteren]

I added a "json" responseType  
http://dvcs.w3.org/hg/xhr/raw-file/tip/Overview.html#the-responsetype-attribute  
and JSON response entity body description:  
http://dvcs.w3.org/hg/xhr/raw-file/tip/Overview.html#json-response-entity-body  
This is based on a proposal by Gecko from a while back.

I tied it to UTF-8 to further the fight on encoding proliferation and  
encourage developers to always use that encoding.


--
Anne van Kesteren
http://annevankesteren.nl/