specify the header fields with ABNF
Reorganise to make hints top-level
appear not to be using browser hints; can bring back if this changes.
move server selection up
move interaction with caches up
"advertising support for client hints"
add accept-CH registration
tweak "server processing of client hints"
tweak IANA considerations
Merge pull request #22 from mnot/edits2

Edits2
small cleanup

- confirmation is a MUST only for some hints
- RW hint is an integer (1*DIGIT)
- drop srcN reference
regenerate draft
update readme

- description from new draft
- link to blink-dev intent to implement
fix formatting
interaction with picture element
fix GA beacon page name (doh)
cleanup picture interop examples
switch to 400px width in example 4 + add Vary
replace % with vw units, closes #26
bump date