Add findlib support

[xavierleroy]

Some packages for CamlIDL include findlib support, sometimes with issues: https://caml.inria.fr/mantis/view.php?id=7125 .

Consider adding findlib support to the master sources.

[ygrek]

Do you want to switch fully to install via ocamlfind install? (idk if there are concerns wrt windows users)
At least (and very easy) it would be nice to move META file to this repo to avoid fixes in opam-repository (ref ocaml/opam-repository#16179)

[xavierleroy]

Apologies for the late reply, I missed your comment in a flurry of Github messages.

I think we need to keep a traditional install for Windows users at least. Perhaps we could have two "install' entries in the Makefile, one with findlib, the other without?

[rwmjones]

FWIW Fedora has been bundling this META file (originally from Debian). The @VERSION@ part is rewritten during the install. https://src.fedoraproject.org/rpms/ocaml-camlidl/blob/master/f/META.camlidl.in