Support zip archives not starting at zero offset (#346)

* Support zip archives not starting at zero offset

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.

* Use updated miniz version

The new miniz version correctly computes the archive starting offset.

* Fix compilation errors

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

* Address some fixes

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Co-authored-by: Kuba Podgórski <[email protected]>