- Accept (lists of) source packages as well as binary packages

- Accept (lists of) package names, and retrieve changelogs from
  get-changelog.cgi or similar (when it works).  In order for this to
  really work in apt mode, we need for apt to implement wishlist bug
  #80123.

- Use dpkg-parsechangelog once it's fixed to accept piped/gzip input
  (bug #80142).  This is not yet feasible because of bug #95579:
  dpkg-parsechangelog loses information.

- Multi-level sort: upload urgency, package priority, package name, what else?

- Make better use of python-apt
  control file parsing
  tar extraction