Add support for Zip archives
    
    If the archive filename ends with `.zip`, use `unzip` rather than
    `tar` to test and extract.
    
    ```
    $ opam2rpm camlzip
    Archive:  /home/michel/.cache/opam2rpm/src/camlzip-rel110.zip
    61b7f60b29d6a432b303b978a95e9262f27a969e
       creating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/.depend
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/.gitignore
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/Changes
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/LICENSE
     extracting: /home/michel/.cache/opam2rpm/src/camlzip-rel110/META-camlzip
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/META-zip
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/Makefile
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/README
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/gzip.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/gzip.mli
       creating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/test/
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/test/Makefile
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/test/minigzip.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/test/minizip.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/test/testzlib.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/zip.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/zip.mli
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/zlib.ml
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/zlib.mli
      inflating: /home/michel/.cache/opam2rpm/src/camlzip-rel110/zlibstubs.c
    Upstream license tag LGPL-2.1-or-later translated to LGPLv2+
    ```
    
    Fixes #5.
    
    Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>