Added script to call for checking mail. Will run individual pre- and
post-hooks. (By default, imapfilter and notmuch update.)
Simple options can be changed through environment variables:
Hooks can be set to different scripts with MBSYNC_PRE and
MBSYNC_POST, respectively.
Will also run mbsync repeatedly, until it exits without error. By
default it will try running it 3 times before giving up, this can be set
with MBSYNC_MAX_TRIES.
No functional imapfilters have been added yet.
mbsync and imapfilter both adhere to the XDG base directory layout
(somewhat), checking for their option files in .config/{isync,imapfilter}
respectively.
Everything still pending changes, the mail eco-system is hard to
wrap one's head around.
