mod_muc_limits: Add config option to limit to join stanzas only This is a bit more limited in pre-0.11 MUC modules, because it just detects stanzas sent to full JIDs (which would include all presence and nick changes). This option is useful for setups where users are typically unaffiliated, but trusted (e.g. if access to the room is gated through some other means such as password/token auth).

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.