mod_mam: On quota hit, separately delete by time and by item count
This is to work around a possible SQL issue where offsets and time
stamps don't interact correctly.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec