WIN32OLE_EVENT#handler=
Instance Public methods
sets event handler object. If handler object has onXXX method according to
XXX event, then onXXX method is called when XXX event occurs.
If handler object has method_missing and there is no method according to
the event, then method_missing called and 1-st argument is event name.
If handler object has onXXX method and there is block defined by #on_event('XXX'){},
then block is executed but handler object method is not called when XXX