first cut at draft-2

- Split CH header into multiple CH-{name} pairs (issue #14)
- Define Accept-CH opt-in mechanism (issue #8)
- Added server hint confirmation section
add remembered site preference opt-in; fixup spelling
Merge branch 'master' into draft2
dropping CH-T (for now)
rework hint-syntax section

- hint can be a single numeric/boolean value (e.g. CH-DPR: 2)
- hint can be a list of values (e.g. CH-X: y=3,z=5)
build latest drafts
fix drp typo
add http-equiv wording
regenerate spec
added display width and clarified server selection
regenerate 01 spec