[Feat] Message verification and signing

Hey,

I think adding message verification and signing would be a nice addition to this library.

As I need to sign some content using the users Wif or private key for a DApp v2.

Wouldn’t mind implementing this.

An API along the lines

const signature = Neon.create.signMessage('PrivateKeyOrWiff', 'Hello World')
const verified = Neon.create.verifyMessage('NeoAddress', 'Hello World', signature)

or

const account = new wallet.Account(privateKey)
const signature = account.signMessage('Hello World')
const verified = Neon.get.verifyMessage('NeoAddress', 'Hello World', signature)

Thoughts or suggestions?

[said-ali]

Within the wallet module.

message.js

/**
 * Generates a signature of the message based on given private key.
 * @param {string} message 
 * @param {string} privateKey
 * @return {string} Signature
 */
export const signMessage = (message, privateKey) => {
  /// Sign and generate message signature using elliptic p256
}

/**
 * Verifies signature matches message and is valid for a given public key.
 * @param {string} message
 * @param {string} signature
 * @param {string} publicKey
 * @return {boolean}

 */
export const verifyMessage = (message, signature, publicKey) => {
  // verify publicKey, message, signature match using elliptic p256
}

api usage:

let signature = Neon.sign.message('Hello', 'private key')
let verified = Neon.verify.message('Hello', signature,  'public key')

What do you think? any remarks?

[snowypowers]

Thanks for your contribution!