code: public static final String prettyPrint(final String binaryString, final char separator) {
      String paddedBinaryString = zeroPadString(binaryString);
      List<String> splitted = Splitter.fixedLength(4).splitToList(paddedBinaryString);
      return Joiner.on(separator).join(splitted);
    }
docs: Returns {@code binaryString} zero-padded separated by {@code seaparator} in groups of 4.