New tunnel protocol

I've revised the draft.

Changes are largely cosmetic.  The document has more complete
boilerplate, including an IANA considerations section.

https://tools.ietf.org/rfcdiff?url2=draft-ietf-httpbis-tunnel-protocol-01.txt

I also created some bad formatting.  I'm correcting that in the
editor's copy, but won't burden people with too many updates at once.