Update to HTTP/2 draft -14.

[Lukasa]

HTTP/2 draft -14 has been released, we should bring ourselves up to date. The RFC is here. We have the following work to do:

• Frame header format is changed (section 4.1). Changes are:
  • No leading reserved bits (previously 2).
  • Length is 24 bits, not 14.
• New settings: SETTINGS_MAX_FRAME_SIZE and SETTINGS_MAX_HEADER_LIST_SIZE (section 6.5.2). (Tracking issues for features: Enable processing for SETTINGS_MAX_FRAME_SIZE. #69 and Enable processing for SETTINGS_MAX_HEADER_LIST_SIZE. #70.)
• END_SEGMENT flag was removed from DATA frames.
• END_SEGMENT flag was removed from HEADERS frames.
• We may get two sections of HEADERS frames at the start: the first one containing a 1XX status code. We'll probably ignore this for now, our API has no good way to handle 1XX and we need to consult with others. (Ignored, tracked in Come up with an API for 1XX responses. #71.)

This set of changes is pretty minor. Should be able to be worked on while I'm in NYC.

[Lukasa]

Initial work here has been pushed, Travis is running now.

[Lukasa]

Done. =D