Exposed with-zipfile-stream outside of package.

[peoplestom]

It doesn't appear to be used anywhere internally, I assume it was
intended to be part of the public API initially.

I needed it to process downloaded ZIP archives in memory i.e.

(zip::with-zipfile-stream (file (flexi-streams:make-in-memory-input-stream in-mem-usb8-vector))
        (zip:do-zipfile-entries (name entry file)
          (format t "~a ~a ~a~%" name entry (zip:zipfile-entry-contents entry))))