Emit action.

def emit(self, action, payload, level=Level.INSTANT):
        """Emit action."""
        if level == self.Level.INSTANT:
            return self.emit_instantly(action, payload)
        elif level == self.Level.CONTEXTUAL:
            return self.emit_contextually(action, payload)
        elif level == self.Level.DELAY:
            return self.emit_delayed(action, payload)
        else:
            raise Exception('InvalidEmitLevel: %s' % level)