This is a major overhaul. Among others it includes the following
changes:

* Split up maildirproc script into multiple modules
* Python project renamed to mailprocessing
* imapproc: mail processing for remote IMAP folders with header cache
* New methods for mail classes:
  * is_seen()
  * is_flagged()
  * strict_mailing_list()
* Added documentation on all the new functionality