turn contributors into editors for MARC (see e.g. https://forums.zotero.org/discussion/34653/editors-of-books-not-downloading-correctly-with-iiimillennium-catalog-translator/#Item_3 we're already doing this in some library catlog translators, no reason not to unify that)

push timestamp

more efficient loops
Merge pull request #675 from adam3smith/marceditor

 turn contributors into editors for MARC