Change for issue #3 - Added Bip38 encryption

As discussed in issue #3 - we love this wallet generator, but it lacks BIP0038 support.. I'd love to create a paper wallet, and then print a copy of it and give it to my friend/brother for safe storage, while not worrying that someone might take the money off the wallet.

I've taken the encryption code taken directly from the live bitaddress.org version