code: func (c *Client) SendToAddressAsync(address btcutil.Address, amount btcutil.Amount) FutureSendToAddressResult {
  	addr := address.EncodeAddress()
  	cmd := btcjson.NewSendToAddressCmd(addr, amount.ToBTC(), nil, nil)
  	return c.sendCmd(cmd)
  }
docs: // SendToAddressAsync 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 SendToAddress for the blocking version and more details.