Implement draft11

[nwgh]

Here's the protocol-level implementation of draft11. All tests pass, new tests have been added where appropriate.

The one major change I didn't do is actually implementing the priority scheme on the connection (in other words, actually prioritizing streams). I felt that was an OK tradeoff to make, since the new prioritization scheme is still in flux, and all priorities are advisory, anyway :) Once we get prioritization more locked-in in the spec, I'll fix up the implementation of prioritization. Right now, this just means that all streams will have the same priority (or one less, for pushed streams).

I'll also be sending a PR to node-http2 to update the version of the protocol library used.

[molnarg]

Thanks, you are the best! The actual prioritization is something that was quite tricky get right back in the summer because of dealing with the Stream class internals, etc. Leave it to me, I'll take care of it when things calm down (maybe the next draft?), this is not critical for Firefox testing right? This time I'll really try to allocate some time to it!

[nwgh]

Thanks! I try to be helpful :) Prioritization is in no way critical for Firefox testing at this point. Perhaps, if we at some time in the future, try to write performance tests, it might become critical for Firefox testing, but given that all PRIORITY frames are advisory, we can't rely on any server doing what we want, anyway.

If I get to draft12 before you, I'll just focus on the protocol bits and leave priority for you.