2 * do not stop on first old item, consume whole feed
3 channel pubDate is not old.
4 * check whether new items are retrieved, but old ones are
6 * item overwrite only if date >= olddate
7 else notice, skip offending item, and do not change
8 feed date, continue but exit with error
9 (invariant: date of every unfetched item is > feed date)
10 * Make directories/items read-only.
11 * check whether dates are handled properly (timezones!)
12 * fix remaining bugs (see README)
13 * support lastBuildDate and pubDate for channels
14 * replace assertions by proper error handling
15 * clean state after a tag level is left, so we can pipe
16 multiple streams, one after another, into one instance.