HTTP/2.0 draft 14 update (frames)

Resolves (at least partly) issue #1015.

Update the HTTP 2.0 Variant to support HTTP/2.0 draft 14, in which the [frame layout changed](http://tools.ietf.org/html/draft-ietf-httpbis-http2-14#section-4.1) from the previous draft.

One thing I'm confused by is that the new frame header is supposed to be 9 octets. I can see where 8 of them (type, flags, padding, reserved bit, stream identifier) are, but I can't figure out where the 9th one is.
mixing words and semantics here is a step back imho. before, this was code to read the frame header, then the below block parsed it. Now, it is read some aribitrary bytes, then the flags, then more arbitrary bytes. I think it is clearer maybe to add a comment of what it was doing before, which I admit may not have been clear. After that, parse the frame header similar to how it was parsed.