*`toV3(password, [options])` - return the wallet as a JSON string (Version 3 of the Ethereum wallet format)
All of the above instance methods return a Buffer or JSON. Use the `String` suffixed versions for a string output, such as `getPrivateKeyString()`.
### Remarks about `toV3`
The `options` is an optional object hash, where all the serialization parameters can be fine tuned:
- uuid - UUID. One is randomly generated.
- salt - Random salt for the `kdf`. Size must match the requirements of the KDF (key derivation function). Random number generated via `crypto.getRandomBytes` if nothing is supplied.
- iv - Initialization vector for the `cipher`. Size must match the requirements of the cipher. Random number generated via `crypto.getRandomBytes` if nothing is supplied.
- kdf - The key derivation function, see below.
- dklen - Derived key length. For certain `cipher` settings, this must match the block sizes of those.
- cipher - The cipher to use. Names must match those of supported by `OpenSSL`, e.g. `aes-128-ctr` or `aes-128-cbc`.
Depending on the `kdf` selected, the following options are available too.
For `pbkdf2`:
-`c` - Number of iterations. Defaults to 262144.
-`prf` - The only supported (and default) value is `hmac-sha256`. So no point changing it.
For `scrypt`:
-`n` - Iteration count. Defaults to 262144.
-`r` - Block size for the underlying hash. Defaults to 8.