cash_addr format implementation inspired by bchaddrjs.
use bch_addr::Converter;
let converter = Converter::new();
let cash_addr = converter.to_cash_addr("1B9UNtBfkkpgt8kVbwLN9ktE62QKnMbDzR").unwrap();
assert_eq!(cash_addr, "bitcoincash:qph5kuz78czq00e3t85ugpgd7xmer5kr7c5f6jdpwk");
let legacy_addr = converter.to_legacy_addr(&cash_addr).unwrap();
assert_eq!(legacy_addr, "1B9UNtBfkkpgt8kVbwLN9ktE62QKnMbDzR");