Adds a callback to the event specified by name

        once <bool> if True the callback will be removed once it's been
        triggered

def on(self, name, callback, once=False):
        """
        Adds a callback to the event specified by name

        once <bool> if True the callback will be removed once it's been
        triggered
        """
        if name not in self.event_listeners:
            self.event_listeners[name] = []

        self.event_listeners[name].append((callback, once))