BIP47 version 1

https://github.com/OpenBitcoinPrivacyProject/bips/blob/master/bip-0047.mediawiki#version-1

Simple v1 BIP47 functionality in Dart

Based mainly on the following: https://github.com/sparrowwallet/drongo/tree/master/src/main/java/com/sparrowwallet/drongo/bip47 https://github.com/Samourai-Wallet/ExtLibJ/tree/3b9832954d3754baaca3307ecc6a872f5aa5d9bc/java/com/samourai/wallet/bip47

Note: Use at your own risk