crypto: ed25519: impl Hierarchical Derivation Keys
Try to reimplement this example: https://github.com/tarassh/ed25519_hd_key/blob/master/src/lib.rs
Based on this RFC: https://github.com/satoshilabs/slips/blob/master/slip-0010.md
Also look at: https://github.com/w3f/hd-ed25519/blob/master/src/lib.rs