make geopub/leaflet a separate library

leaflet.opam

@@ -0,0 +1,33 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+synopsis: "OCaml library/executable to TODO"
+description: "leaflet is an OCaml library/executable to TODO."
+maintainer: ["TODO"]
+authors: ["TODO"]
+license: "ISC"
+tags: ["leaflet" "TODO" "TODO" "TODO" "TODO"]
+homepage: "TODO/leaflet"
+doc: "TODO/leaflet"
+bug-reports: "TODO/leaflet"
+depends: [
+  "dune" {>= "2.9"}
+  "ocaml" {>= "4.08"}
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "--promote-install-files=false"
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+  ["dune" "install" "-p" name "--create-install-files" name]
+]
+dev-repo: "TODO/leaflet"