minor work on HTTP problem -03
relation to HTTP OPTIONS should be clarified
updated RFC4288 to RFC6838
Remove comments; break long lines; restore XML decl
update year
3023 is non-normative.
Incorporate Erik's changes

 - add RFC6838 reference
 - add elementFormDefault to schema
 - add Erik as an author
Move from describing in terms of the JSON format to just using it for the data model.
mention XML media type a bit earlier
more text about when to mint and when to reuse
turning all URL into URI; other minor edits
media type changes
added some intro, made the text a little less JSON-only
minor edit
made schema a bit more compact
merging mark's changes
changed to ASCII apostrophes
switching from XSD to RNG
switched from XSD to RNG
minor work on HTTP problem -03