code: function getChar (bits) {
    var index = parseInt(bits,2);
    if (isNaN(index) || index < 0 || index > 63) throw new Error('baseURL#getChar: Need valid bitString');
    return ALPHABET[index];
  }
docs: Get baseURL char from given 6bit bitstring
  @param  {string} bits  6bit bitstring
  @return {string}       baseURL char