rsync for IMAP4, mbox, and maildir

NOTE: msync is a work-in-progress, currently it can only transfer from mbox/maildir to IMAP. Eventually it will be able to transfer between any of the supported formats.

The arguments are modelled after rsync somewhat, both source and destination take the form of protocol://[username:password@host:port]/folder. For example, to copy from a local MBOX file to an IMAP server:

msync.py 'mbox://./sent_mail.mbox' 'imap://me@example.com:abc123@imap.example.com:143/Sent Mail'