void on_tick()

This event is called on all AI modules on a living approximately once every
30 seconds. It is called by the living object's heartbeat and thus will
scale time with system lag. This is meant to prevent runaway AI modules from
killing cpu resources.

Writing AI modules with faster ticks of their own is discouraged for this
reason. If a module needs to perform some particular action more frequently,
there is a good chance that an appropriate event is already being fired off
for just that eventuality.
