fix examples broken by recent event wait/clear changes

This fixes #12 as raised by @mention vmayoral.

I'd really like to change the way that the wait/clear stuff is interfaced.  It seems that we should make variants of wait/clear methods that do an auto lookup of the host_interrupt given the system event (instead of necessarily specifiying the host_interrupt.  This can be implemented using the lookup routines that I added earlier to (re)discover the mapping of event/channel/interrupt.