Split mod_mam into mod_mam and mod_mam_muc. Extracted a part of code into mod_mam_dump. Changed configuration semantics. Pass UserID (ArcID) as a parameter of back-end modules' functions.
Removed muc.localhost from hosts.
Run mod_mam_muc on the same server's host as all other modules. Wrote mod_mam_muc_async_writer:wait_flushing/4.