mod_sasl2_bind: Support for Bind 2.0 with SASL2
This is based on an experimental in-progress derivative of the current
XEP-0386.
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.