Consistently use "error code" instead of "status code" for stream and session related errors
Changed stream priority to be 31 bits long instead of 3 bits.
SETTINGS related changes as proposed in Tokyo

Added a note that settigs persistence might be removed in a future version.
Added a requrement on both sides to send SETTINGS as the first frame
after establishing an HTTP/2.0 connection.

Also added placeholder for the "magic" sequence before sending any frames.
Merge branch 'master' of github.com:http2/http2-spec
Major editorial cleanup for frame header changes.
Updating .html with changes.
Merging (with apparently no change).