keys/hd/address.go
func CalcHash256(data []byte) []byte {
	return CalcHash(CalcHash(data, sha256.New()), sha256.New())
}
func CalcHash256(data []byte) []byte {
	return CalcHash(CalcHash(data, sha256.New()), sha256.New())
}
// CalcHash256 returns the sha256(sha256(data)).