code: func NewAlphabet(s string) *Alphabet {
  	if len(s) != 58 {
  		panic("base58 alphabets must be 58 bytes long")
  	}
  	ret := new(Alphabet)
  	copy(ret.encode[:], s)
  	for i := range ret.decode {
  		ret.decode[i] = -1
  	}
  	for i, b := range ret.encode {
  		ret.decode[b] = int8(i)
  	}
  	return ret
  }
docs: // NewAlphabet creates a new alphabet from the passed string.
  //
  // It panics if the passed string is not 58 bytes long or isn't valid ASCII.