update the doc of Map.(add, remove, filter)
update the doc of Map.(add, remove, filter)

eliberis/ocaml,msprotz/ocaml,yunxing/ocaml,eliberis/ocaml,gerdstolpmann/ocaml,yunxing/ocaml,yunxing/ocaml,yunxing/ocaml,yunxing/ocaml,eliberis/ocaml,msprotz/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,eliberis/ocaml,gerdstolpmann/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,msprotz/ocaml,eliberis/ocaml