code: def key_release_event(self, widget, event):
          
          # get keyname or keycode and translate to ginga standard
          # keyname =
          # keycode =
          keyname = ''  # self.transkey(keyname, keycode)
          self.logger.debug("key release event, key=%s" % (keyname))
          return self.make_ui_callback('key-release', keyname)
docs: Called when a key is released after being pressed.
          Adjust method signature as appropriate for callback.