Remove per-frame compression
Ignore unknown frame types

Unexpected CONTINUATION frame is handled separately as connection
error.
Make settings_id 2 bytes field
Ignore unknown settings ID
Remove PAD_HIGH and Pad High field

CONTINUATION now doesn't have padding.
Allow transmission and reception of PRIORITY frame to a closed stream
Check stream_id is nonzero for DATA, HEADERS, PRIORITY, RST_STREAM, PUSH_PROMISE
Remove bogus comments
Remove reserved field from ALTSVC frame
Set HTTP/2 protocol id to h2-13 for now
Separate extension frames from core frames

ALTSVC and BLOCKED frames are now extension frames.  To add new
extension frame without modifying nghttp2_frame union, which causes so
name bump, we separated extension frames from core frames.
nghttp2_frame includes generic nghttp2_extension.  The payload member
of nghttp2_extension will point to the structure of extension frame
payload.  The frame types of extension frames are defined in
nghttp2_ext_frame_type.
Fix compile error with --enable-debug
Fix unused header_cb_arg structure
Refactor storage of settings

Now local and remote settings values are stored in dedicated structure
nghttp2_settings_storage.
Make return type of inbound_frame_set_settings_entry void
Merge branch 'master' into h2-13

Conflicts:
	lib/nghttp2_session.c
nghttpx: Only allow DHE, ECDHE + AEAD ciphers for HTTP/2

Cipher suites are chosen by DHE and ECDHE ciphers + GCM (AEAD).  Now
default cipher list is the one recommended by Mozilla web site.  The
--honor-cipher-order option is removed and now it is always assumed.
nghttpx: Create NPN prefs only once
nghttpx: Don't check TLS requirement in ALPN cb cause cipher obj is nullptr

Also don't compare ALPN identifier with streq, since they are just
byte string.
nghttpx: Drop connection if HTTP/2 security level is not satisfied on frontend