fix content hash issues for json. do not
hash url/resolved_url/html fields. do exact
order-independent hashes of remaining field/value pairs.
used for setting EDOCUNCHANGED and doing spidertime/querytime
deduping. also do not index "html" json field because it
is huge, slow and redundant. convert "date" field
into a number so we can sort/constrain by article pub date.