ACK flag and use for Header Table size updates

Adds the ACK flag to SETTINGS with a section on settings
synchronization.  Moves the SETTINGS_HEADER_TABLE_SIZE setting into the
core spec, and replaces it with a brief recap of how synchronization
applies to compressor context.  Also renames the PONG flag for
consistency.
Changelist

Added changes to change list and reworded based on Martin's feedback.
Merge remote-tracking branch 'upstream/master' into settings_ack

Conflicts:
	draft-ietf-httpbis-http2.xml
ACK flag and use for Header Table size updates

Adds the ACK flag to SETTINGS with a section on settings
synchronization.  Moves the SETTINGS_HEADER_TABLE_SIZE setting into the
core spec, and replaces it with a brief recap of how synchronization
applies to compressor context.  Also renames the PONG flag for
consistency.
Resolving merge conflict.
Merge branch 'settings_ack' of https://github.com/MikeBishop/http2-spec into settings_ack
Merge pull request #271 from MikeBishop/settings_ack

Settings ACK. Fixes #120.