Add an opportunity to derive addresses from master public keys

[selevit]

The problem is explained here: https://community.libra.org/t/libra-bip32-addresses-proposal/1934

I’ve created an example in Python how to derive new Libra address from master public key and then send coins from this address: https://github.com/selevit/libra_bip32 Would be great to implement this approach in your awesome library.

Thanks a lot for the great job!

[yuan-xy]

I read your code, it works. I think maybe you can make a pull request based on it.

1. Write a new KeyFactory class.
2. implement libra_bip32 key derivation.
3. write test code

[selevit]

So, I can do it, but a little bit later. Will let you know when it's ready!