code: function(str, n) {
      var result = '';
      n = n || 0;
      stringCodes(str, function(c) {
        result += chr(c + n);
      });
      return result;
    }
docs: *
  @method shift(n)
  @returns Array
  @short Shifts each character in the string `n` places in the character map.
  
  @example
  
  'a'.shift(1)  -> 'b'
  'ク'.shift(1) -> 'グ'
  
  @param {number} n
  
  *