code: def add_event_callback(self, pin, callback, bouncetime=-1):
          
          kwargs = {}
          if bouncetime > 0:
              kwargs['bouncetime']=bouncetime
          self.bbio_gpio.add_event_callback(pin, callback, **kwargs)
docs: Add a callback for an event already defined using add_event_detect().
          Pin should be type IN.  Bouncetime is switch bounce timeout in ms for 
          callback