[Idea] HDKey generation

[mistermoe]

it'd be cool if the ssi-sdk allowed for creation of HDKeys / recovery from them. basically a method or series of methods that allowed someone to:

• generate a mnemonic based on some entropy
• create a master seed based on that mnemonic
• generate root and derive keys based on a BIP44 style derivation path

i imagine mobile will need this for baseline key mgmt

ssi-sdk has this currently, but i think there will be many scenarios where a derived key is more desired than a "willy nilly" one.

mnemonics are kinda all we have w.r.t recovery atm.

applies to secp256k1 and Ed25519

[sondreb]

I know this SDK is Go, but for reference it appears that @paulmillr have gotten around to make an HD-key derivation package for Ed25519: https://github.com/paulmillr/ed25519-keygen#hdkey

This will be useful for other repos and maybe the implementation can be replicated directly in the SDK?