2.3. Member format

      Each member has the following structure:

         +---+---+---+---+---+---+---+---+---+---+
         |ID1|ID2|CM |FLG|     MTIME     |XFL|OS | (more-->)
         +---+---+---+---+---+---+---+---+---+---+

      (if FLG.FEXTRA set)

         +---+---+=================================+
         | XLEN  |...XLEN bytes of "extra field"...| (more-->)
         +---+---+=================================+

      (if FLG.FNAME set)

         +=========================================+
         |...original file name, zero-terminated...| (more-->)
         +=========================================+

      (if FLG.FCOMMENT set)

         +===================================+
         |...file comment, zero-terminated...| (more-->)
         +===================================+

      (if FLG.FHCRC set)

         +---+---+
         | CRC16 |
         +---+---+

         +=======================+
         |...compressed blocks...| (more-->)
         +=======================+

           0   1   2   3   4   5   6   7
         +---+---+---+---+---+---+---+---+
         |     CRC32     |     ISIZE     |
         +---+---+---+---+---+---+---+---+