Divide by XlogID (256 files per subdir)
Example:

00000000
      |   -> 000000010000000000000001
      |   -> 000000010000000000000002
      ...
00000001
      |   -> 000000010000000100000000
      |   -> 000000010000000100000001
      ...

TODO:

• multi-thread support for show --archive
• optimize subdirectory creation in archive-push
• fix tests
• add more compatibility and delete tests