message: add function to convert from private to public setting
diff: @@ -398,6 +398,14 @@ impl AddressGenerator<XPrv> {
  }
  }
  + pub fn public(self) -> AddressGenerator<XPub> {
  + AddressGenerator {
  + hdkey: self.hdkey,
  + cached_key: self.cached_key.public(),
  + derivation_scheme: self.derivation_scheme,
  + }
  + }
  +
  fn key(&self, path: &Addressing) -> XPrv {
  self.cached_key
  .derive(self.derivation_scheme, path.0)
  