pub fn combine_pk_and_chaincode(
key: PublicKey<Ed25519>,
chaincode: &[u8]
) -> Result<PublicKey<Ed25519Bip32>, PublicKeyError>
pub fn combine_pk_and_chaincode(
key: PublicKey<Ed25519>,
chaincode: &[u8]
) -> Result<PublicKey<Ed25519Bip32>, PublicKeyError>