Now imapsql module does not handle authentication. (it was not doing it so well
anyway)
sql_table module was introduced and used in the default configuration as
a replacement for functionality that was implemented by imapsql before.
Parts of maddyctl code were rewritten to make it work transparently with
any IMAP backend or credentials store.
Closes#212.
Several comments were removed since they are not worth the trouble.
A few minor issues were addressed.
Most of remaining comments got corresponding GitHub issues assigned.
