Adding to change log.
update contributing section
Merge branch 'master' of github.com:http2/http2-spec
fix markdown?
Merge branch 'layering' of github.com:http2/http2-spec into layering
Tweaking header block text.
Moving stuff to HttpExtra section.  Clarifying, rewording and reformatting server push section.  Removing HEAD push, for now.
Formatting tweaks.
fix xml tag
editorial fix of half closed states
add :scheme in HTTP Request examples
Merge branch 'layering' of github.com:http2/http2-spec into layering
some minor editorial clean-up
Merge pull request #157 from shigeki/shigeki_20130702

some editorial fixes
Clarifying examples.  Editorial fixups.
Editorial cleanup, courtesy @jpinner.
Editorial corrections
Flow control corrections
State diagram correction
Fixing typo