introduction to the TPE

Apologies for having to drop in the middle of this discussion today, but 
I was late for another meeting. As we discussed, the Introduction should 
be pared down to remove unneeded and inappropriate text, and to better 
reflect what is in the document. The last para is most all that's 
required. I propose the following version as the complete intro:

/1. Introduction//
/

/This specification defines protocol elements for use within the 
Hypertext Transfer Protocol [/HTTP 
<http://www.w3.org/2011/tracking-protection/drafts/tracking-dnt.html#bib-HTTP>/] 
which allow a user to express a tracking preference, via the////DNT 
<http://www.w3.org/2011/tracking-protection/drafts/tracking-dnt.html#dfn-dnt>////request 
header field, and allow a server to describe their tracking behavior via 
a well-known////tracking status resource 
<http://www.w3.org/2011/tracking-protection/drafts/tracking-dnt.html#status-resource>////and 
the////Tk 
<http://www.w3.org/2011/tracking-protection/drafts/tracking-dnt.html#dfn-tk>////response 
header field. In addition, JavaScript APIs are defined for enabling 
scripts to determine DNT status and to register a user-granted 
exception. This specification does not stand on its own, but rather is 
intended to couple with a compliance specification that will define what 
recipients must do in response to the DNT request header field./