Simple archiving program emulating functionality of Thunderbird on plain IMAP server.

All messages older than given number of days are moved to the
corresponding archive folder in the year-rooted hierarchies. So,
for example a message from `Computer/python` could get moved to
`Archive/2018/Computer/python`.

All issues, questions, complaints, or (even better!) patches
should be send via email to [me](mailto:mcepl@cepl.eu) email list
(for patches use [git send-email](https://git-send-email.io/)).