Add a derivation for ocaml-calendar

pkgs/development/ocaml-modules/calendar/default.nix

@@ -0,0 +1,23 @@
+{stdenv, fetchurl, ocaml, findlib}:
+
+stdenv.mkDerivation {
+  name = "ocaml-calendar-2.03.2";
+  src = fetchurl {
+    url = https://forge.ocamlcore.org/frs/download.php/915/calendar-2.03.2.tar.gz;
+    sha256 = "04pvhwb664g3s644c7v7419a3kvf5s3pynkhmk5j59dvlfm1yf0f";
+    };
+
+  buildInputs = [ocaml findlib];
+
+  createFindlibDestdir = true;
+
+  meta =  {
+    homepage = https://forge.ocamlcore.org/projects/calendar/;
+    description = "An Objective Caml library managing dates and times.";
+    license = "LGPL";
+    platforms = ocaml.meta.platforms;
+    maintainers = [
+      stdenv.lib.maintainers.gal_bolle
+    ];
+  };
+}