message: add a way to create simple addresses
diff: @@ -294,6 +294,11 @@ impl ExtendedAddr {
  }
  }
  + // bootstrap era + no hdpayload address
  + pub fn new_simple(xpub: XPub) -> Self {
  + ExtendedAddr::new(AddrType::ATPubKey, SpendingData::PubKeyASD(xpub), Attributes::new_bootstrap_era(None))
  + }
  +
  /// encode an `ExtendedAddr` to cbor with the extra details and `crc32`
  ///
  /// ```
  