Tarix now supports compressing the tar file with zlib (a.k.a. gzip).  To
enable this mode, use the -z option, and optionally a compression level.

Tarix will specially construct the output so that it is compatible with
gzip, but also so that tarix can have sufficient random access within
the file to perform selective extraction.

When extracting the compressed archive, you can either decompress it first,
or use the -z option to work directly with the compressed archive.

Even though the compressed archive will be compatible with gzip, you will
not be able to simply gzip an archive and use it with tarix.  Gzip won't
include the synchronization points tarix needs for random access.
