fetcher: Update the way the RSS library parser fetches feeds.
fetcher: Update the way the RSS library parser fetches feeds.

In the previous approach, all previously seen feed metadata was cached, which is unnecessary and wasteful in terms of memory, which would grow unboundedly (but slowly).

jrupac/goliath,jrupac/goliath,jrupac/goliath,jrupac/goliath,jrupac/goliath