code: public T maxLength(int max) {
          if (isEmpty()) return _empty();
          if (length() < (max - 3)) return me();
          return subList(0, max).append("...");
      }
docs: <p>Return a string no longer than specified max length.
  <p>If the string supplied is longer than the specified max length
  then only it's part that is less than the max length returned, appended
  with "..."
  
  @param max the maximum length of the result
  @return A StrBase instance that contains at most `max` number of chars of this instance