Make odate work with OCaml >4.06 and OPAM >2.0 (#5)

* Use new-style Stdlib rather than Pervasives.

* Update the opam file for opam 2.x

odate.opam

@@ -1,16 +1,23 @@
-opam-version: "1.2"
+opam-version: "2.0"
 maintainer: "[email protected]"
 authors: [ "Hugo Heuzard" ]
 license: "LGPL-2.1 with OCaml linking exception"
 homepage: "https://github.com/hhugo/odate"
 build: [
-  ["dune" "build" "--only" "odate" "--root" "." "-j" jobs "@install"]
+  ["dune" "subst"] {pinned}
+  ["dune" "build" "-p" name "-j" jobs]
 ]
 depends: [
+  "ocaml" {>= "4.07.0"}
   "dune" {build}
   "menhir" {build}
   "base-unix"
 ]
+synopsis: "Date & Duration Library"
+description: """
+Simple date and duration manipulation. Also implement duration printer
+based on string format. Already implemented in opalang
+[http://opalang.org/]. For documentation about the format, see :
+[http://doc.opalang.org/value/stdlib.core.date/Duration/try_generate_printer].
+"""
 dev-repo: "git://github.com/hhugo/odate"
-available: [ ocaml-version >= "4.00.0" ]
-

src/duration_private.ml

@@ -1,4 +1,4 @@
-module P = Pervasives
+module P = Stdlib
 
 module O : sig
 

src/oDate.ml

@@ -939,7 +939,7 @@ end
 module MakeImplem(C : Clock) : Implem = struct
   type t = float
 
-  let compare = Pervasives.compare
+  let compare = Stdlib.compare
 
   let add f i = f +. i
   let from_seconds x = x