message: also check signature is correct here
diff: @@ -1085,6 +1085,11 @@ struct TestVector {
  let xpub = xprv.public();
  let ref_xpub = XPub::from_slice(test.xPub).expect("failed to read the xpub from the test");
  assert_eq!(ref_xpub, xpub, "xpub from test {}", test_index);
  +
  + let ref_signature : Signature<Vec<u8>> = Signature::from_slice(test.signature)
  + .expect("retrieve signature from the golden test");
  + let signature = xprv.sign(test.data_to_sign.as_bytes());
  + assert_eq!(ref_signature, signature, "xpub from test {}", test_index);
  }
  #[test]
  