The add-on format is documented in the included headers.  Read them carefully,
as they contain instructions in the comments on certain things that you should
and should not do.  Pay particular attention to the end of the header file
where it tells you what functions you need to implement and export symbols for
in order for your add-on to be used.  This is everything you need to build an
add-on event handler for Scheduler.  There is also a sample add-on included
here.  Email any questions to btietz@biomail.ucsd.edu.

Brian