Given an iterable of CouchDB change notifications and a
GratipayDB, read from the stream and write to the db.
The npm registry is a CouchDB app, which means we get a change stream from it that allows us to follow registry updates in near-realtime. Our strategy here is to maintain open connections to both the registry and our own database, and write as we read.
Return a smoothed-out doc, or None if it’s not a package doc, meaning there’s no name key and it’s probably a design doc, per:
Given a sequence number in the npm registry change stream, start streaming from there!