Modified implementation based on github.com/mr-tron/base58 itself based on https://github.com/trezor/trezor-crypto/blob/master/base58.c

It's nice to have a fast base58 implementation but do we really need to have the slow version in the same lib too?

Usage

// to decode some base58 string
dec, err := base58.Bitcoin.Decode(in)
if err != nil {
    // handle err
}
// or, to encode:
enc := base58.Bitcoin.Encode(dec)