code: func (c *Client) ListUnspentAsync() FutureListUnspentResult {
  	cmd := btcjson.NewListUnspentCmd(nil, nil, nil)
  	return c.sendCmd(cmd)
  }
docs: // ListUnspentAsync returns an instance of a type that can be used to get
  // the result of the RPC at some future time by invoking the Receive function
  // on the returned instance.
  //
  // See ListUnspent for the blocking version and more details.