MINOR: lua: Add act:wake_time() function to set a timeout when an action yields

MINOR: lua: Add act:wake_time() function to set a timeout when an action yields

This function may be used to defined a timeout when a lua action returns
act:YIELD. It is a way to force to reexecute the script after a short time
(defined in milliseconds).

Unlike core:sleep() or core:yield(), the script is fully reexecuted if it
returns act:YIELD. With core functions to yield, the script is interrupted and
restarts from the yield point. When a script returns act:YIELD, it is finished
but the message analysis is blocked on the action waiting its end.