code: public RandomAccessData getCentralDirectory(RandomAccessData data) {
          long offset = Bytes.littleEndianValue(this.block, this.offset + 16, 4);
          long length = Bytes.littleEndianValue(this.block, this.offset + 12, 4);
          return data.getSubsection(offset, length);
      }
docs: Return the bytes of the "Central directory" based on the offset indicated in this
  record.
  @param data the source data
  @return the central directory data