code: func (c *Client) KeyPoolRefillSizeAsync(newSize uint) FutureKeyPoolRefillResult {
  	cmd := btcjson.NewKeyPoolRefillCmd(&newSize)
  	return c.sendCmd(cmd)
  }
docs: // KeyPoolRefillSizeAsync 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 KeyPoolRefillSize for the blocking version and more details.