+ * # #[derive(Clone)]
+ * # struct YourCustomMessage {}
+ * impl Writeable for YourCustomMessage {
+ * \tfn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+ * \t\t# Ok(())
+ * \t\t// Write your custom onion message to `w`
+ * \t}
+ * }
+ * impl CustomOnionMessageContents for YourCustomMessage {
+ * \tfn tlv_type(&self) -> u64 {
+ * \t\t# let your_custom_message_type = 42;
+ * \t\tyour_custom_message_type
+ * \t}
+ * }
+ * Send a custom onion message to a node id.