Zip archives are usually read from the back to the front, making it
possible to append them to other files (e.g. executables) in order to
provide some kind of embedded filesystem.

This PR makes it possible to read, write, and update such zip files
without affecting the existing functionality.

The new miniz version correctly computes the archive starting offset.

Use the correct mkdir signature on Windows vs other platforms.
Remove CHMOD macro, it was simply wrapping the chmod libc call.