Add Account class

[ryanio]

This PR adds a new Account class intended as a modern replacement for ethereumjs-account. It has a shape of Account(nonce?: BN, balance?: BN, stateRoot?: Buffer, codeHash?: Buffer).

Instantiation

The static factory methods assist in creating an Account object from varying data types: Object: fromAccountData, RLP: fromRlpSerializedAccount, and Array: fromValuesArray.

Methods: isEmpty(): boolean, isContract(): boolean, serialize(): Buffer

Example usage:

import { Account, BN } from 'ethereumjs-util'

const account = new Account(
  new BN(0), // nonce, default: 0
  new BN(10).pow(new BN(18)), // balance, default: 0
  undefined, // stateRoot, default: KECCAK256_RLP (hash of RLP of null)
  undefined, // codeHash, default: KECCAK256_NULL (hash of null)
)

For more info see the documentation or examples of usage in test/account.spec.ts.

[coveralls]

Coverage decreased (-0.2%) to 99.527% when pulling e48478d on add-account-class into d8b8e44 on master.

[ryanio]

I couldn't find a way to ignore this file in typedoc without getting the error Could not find a declaration file for module 'ethjs-util'., so I guess there is no harm in having it for now, although I wish the file was filled with the type info rather than just being empty 😅

The library mode in typedoc is pretty new and works quite well for our purposes, so perhaps it will be fixed or improved in the future:

Warning: File ./src/@types/ethjs-util/index.ts is not a module and cannot be converted in library mode

[jochem-brouwer]

Some comments regarding consistency and explicitness. Looks good in general 👍 😄

[holgerd77]

Somewhat comment-focused review, some suggestions for improvements, otherwise looks good.

[holgerd77]

Do we want to add nonce and balance >= 0 checks here as well or is this unnecessary?

[ryanio]

sure, added in b0aacc0

[holgerd77]

Really nice tests. 😄

[holgerd77]

Thanks Ryan, looks really great! Sorry that this took so long to review, fall a bit aside, feel free to be more pushy/demanding here if you need things for subsequent tasks.