mod_muc_moderation: Stamp XEP-0421 occupant-id for the acting moderator Gives clients some hint about which moderator it was who did the deed. The @by attribute does have the nick of the actor, but they could change their nickname at some point, which is what occupant-id solves. Ref #1816

This module logs events where more than a certain amount of CPU time was
spent.

``` lua
log_cpu_threshold = 0.01 -- in seconds, so this is 10 milliseconds
```

Uses the Lua
[`os.clock()`](http://www.lua.org/manual/5.2/manual.html#pdf-os.clock)
function to estimate CPU usage.