Include curve-type when returning public key

[robdefeo]

Is your feature request related to a problem? Please describe.
A public key can be of different types, secp256k1, ed25519, sr25519, with the addition of substrate to send a message it will need to know what curve-type is used to be able to decode it ref #52

Describe the solution you'd like

• Including the key type of the found public key

{
    "public_key": "0x369bb60e6d99e30144e8fab8087bd7d171ba7b5dbf691b87319584b3d6c1892c"
    "curve-type": "secp256k1"
}

• use new return value crypto.PublicKey created by finder.PublicKeyFromAddress should return PublicKey #414
• use Kind created by Add Kind() to public key interface #382

[abadojack]

@robdefeo Can I have this assigned to me?

[robdefeo]

Assigned :) Thanks @abadojack