message: add Clone feature for the Seed
diff: @@ -159,6 +159,13 @@ impl Seed {
  Ok(Seed::from_bytes(v))
  }
  }
  +impl Clone for Seed {
  + fn clone(&self) -> Self {
  + let mut bytes = [0; SEED_SIZE];
  + bytes.copy_from_slice(self.as_ref());
  + Seed::from_bytes(bytes)
  + }
  +}
  impl AsRef<[u8]> for Seed {
  fn as_ref(&self) -> &[u8] { &self.0 }
  }
  