Stop using extension <x:lt>. I don't want to run java.

TODO(willchan): Give up and run java later and fix this. But it's not
worth my time right now to figure that out.
Copy the document organization and definition sections from HTTP2.
As per HTTP2, delete "Use of GOAWAY" section.

It was mostly redundant anyway, although it did offer some useful
explanation.
Copy HTTP2 Connection Management section.

Just formatting changes.
As per HTTP2, update HTTPLayer intro section.

Again, just formatting/editorial changes.
Add new HTTP headers section from HTTP2.
Copy HTTP2's HttpRequest section.

This is mostly formatting & editorial changes. There are two minor
changes of substance:
* Adds text mandating that colon prefixed headers come before all other
  headers.
* Adds text specifying a PROTOCOL_ERROR if a DATA frame comes before the
  stream is opened.
Copy HttpResponse from HTTP2 spec.

Mostly editorial/formatting changes. Some minor changes around error
handling:
* Duplicate ":status" header ==> PROTOCOL_ERROR
* DATA frame before stream open ==> PROTOCOL_ERROR
Copy PushResources intro section from HTTP2 spec.

Just editorial/formatting changes.
Add a NOTE explaining why the Server Implementation section is not
updated.
Copies the server push client implementation section from HTTP2.

Primarily editorial changes. One minor substantial change:
* PUSH_PROMISE without the identifying headers (scheme, etc) results in
  a PROTOCOL_ERROR.
Connection header is now 24 octets, not 25.
GOAWAY Message=>frame.
Merge pull request #24 from willchan/Editorial

Copy the document organization and definition sections from HTTP2.
Merge pull request #26 from willchan/Fixes

Minor fixes
Merge pull request #25 from willchan/HTTPLayer

Copy HTTPLayer from HTTP2 spec
Merge pull request #23 from willchan/FixUselessExtensions

Stop using extension <x:lt>. I don't want to run java.