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.
Hmm, did I misinterpret the diagram? Here's how I look at it:

* First row: 24-bit (3-byte) length, followed by 8 bits (1 byte) of emptiness
* Second row: 8-bit (1-byte) type, 8-bit (1-byte) flags, 16 bits (2 bytes) of emptiness
* Third row: 1-bit reserved, 31-bit stream ID

(On second thought concerning me thinking that the emptiness after the length was the 9th octet, I think I'm wrong because the previous frame iteration does not fit along the scheme I was thinking of.)