- Add option to use manifest file from https://lore.kernel.org/manifest.js.gz
  instead of periodically probing git fetch to check for new mail. This would
  allow to compare "fingerprint" or "modified" entries to see if the repos
  actually changed. The "fingerprint" entry is just `git show-ref | sha1sum`,
  which is deterministic.

- Using the manifest file will additionally help to automatically recognize
  epoch roll-over. It does not happen very frequently, but it does happen --
  0.git will eventually stop being updated and become 1.git, etc. Relying on
  the manifest, one will be able to automatically recognize when such event
  occurs and therefore it wouldn't need to be manually enabled in the l2md
  configuration file.