threadwalker caught up with yesterday's feed change

Ricardo reported on issue #14 that the walker printed ? for every author -- it was still reading the item-level source:account element that came out of the feeds yesterday. Now it reads what the feeds actually say: replies carry a core RSS <source> element naming the author, and in a user's own feed the channel says whose feed it is. Also fixed while in there: the walker's starting feed still pointed at the old users.rss.network address, which now answers with a redirect that Node's bare https.get won't follow -- it points at https://rss.chat/users/manton/rss.xml directly. Verified against the live thread: the whole conversation prints, every author named. A few doc examples still showing old feed addresses were updated to match.