code: function indexOfBits (char) {
    var index = ALPHABET.indexOf(char);
    if (index < 0) throw new Error('baseURL#indexOfBits: Need valid baseURL char');
    return bitString.pad(index.toString(2), 6) ;
  }
docs: Get 6bit bitstring given a baseURL char
  @param  {string} char Single baseURL char
  @return {string}      6bit bitstring of 'indexof' (0-63)