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>