Add a couple more EventResponder comments

teensy3/EventResponder.cpp

 
 void EventResponder::runFromInterrupt()
 {
+	// FIXME: this will fail if the handler function triggers
+	// its own or other EventResponder instances.  The list will
+	// change while we're holding a pointers to it.
 	for (EventResponder *first=firstInterrupt; first; first = first->_next) {
 		first->_pending = false;
 		(*(first->_function))(*first);

teensy3/EventResponder.h

  * for the most immediate response, even if doing so is more difficult.
  * EventResponder lets you choose how your function will be called,
  * without editing the timers or libraries which trigger the events.
+ *
+ * Event handling functions called by EventResponder should complete
+ * their work quickly.  Avoid delays or operations which may take
+ * substantial time.  While your function runs, no other event functions
+ * (attached the same way) are able to run.
+ *
+ * If your EventResponder is triggered more than once before your
+ * function can run, only the last trigger is used.  Prior triggering,
+ * including the status integer and data pointer, are overwritten and
+ * your function is called only one time, based on the last trigger
+ * event.
  */
 
 class EventResponder;