Support Id generation from ed25519 pubkeys

[ebuchman]

As far as I can tell these Id::from methods aren't even being used yet - is that right? In any case, here's the ed25519 one. Also the secp256k1 one is missing a ripemd160 if it's supposed to match Tendermint Core.

Why are these called Id and not Address?

[tarcieri]

As far as I can tell these Id::from methods aren't even being used yet - is that right?

Correct

Also the secp256k1 one is missing a ripemd160 if it's supposed to match Tendermint Core.

Aah, I thought all RIPEMD160 usage had been eliminated. My mistake. Would you like to do a followup PR to fix that?

Why are these called Id and not Address?

I think we debated between account::Address and account::Id and chose the latter for consistency with node::Id, but changing it to Address would make sense.