ENH Update to EdDSA signing key

[mikenuguid]

• Updates to a more secure EdDSA algorithm using Ed25519 curve.
• Unit tests updated to use EdDSA signer and pre-generated key pairs
• Updated ReadMe on how to generate key pairs using Ed25519 algorithm

[blueo]

@mikenuguid does this change the hash method in general? I'm looking at another system that would require a slightly different one - wondering if we make this a configuration option - eg you can pass in which system you want to use.

[mikenuguid]

Thanks for checking @blueo. Configuration sounds a nice. I'll make changes on this when I get some time.

[mikenuguid]

@blueo I've created a new pull request to replace this. Closing this one too. 🙂