code: func (sc *Client) FilterMessages(ctx context.Context, id string) ([]*whisper.Message, error) {
  	var messages []*whisper.Message
  	return messages, sc.c.CallContext(ctx, &messages, "shh_getFilterMessages", id)
  }
docs: // FilterMessages retrieves all messages that are received between the last call to
  // this function and match the criteria that where given when the filter was created.