Convert a TimeEvent object to json format.

def format_time_event_json(self):
        """Convert a TimeEvent object to json format."""
        time_event = {}
        time_event['time'] = self.timestamp

        if self.annotation is not None:
            time_event['annotation'] = self.annotation.format_annotation_json()

        if self.message_event is not None:
            time_event['message_event'] = \
                self.message_event.format_message_event_json()

        return time_event