Draft-08 and Third Implementation Draft Milestones

Hi all!

As expected, we had a bunch of stuff flagged for the 3rd implementation
draft that doesn't appear in -08.

 https://github.com/http2/http2-spec/issues?milestone=3&state=open

(264, 216, 21, 18, 292 at the time of this email.)

That's mostly cool by me - but I'm wondering if we will stretch the overall
process out by not getting the alternate-reference-set stuff (in
particular) into a new draft that is part of the zurich implementation
target. It feels like it could use some experience.

barring further guidance we'll just change -07 to -08 and make it available
for testing.

-P