Update opam file to OPAM 2 format

yojson.opam

@@ -1,22 +1,32 @@
-opam-version: "1.2"
+opam-version: "2.0"
 maintainer: "[email protected]"
 authors: ["Martin Jambon"]
-homepage: "https://mjambon.github.io/mjambon2016/yojson-doc/Yojson.html"
-bug-reports: "https://github.com/mjambon/yojson/issues"
-dev-repo: "https://github.com/mjambon/yojson.git"
-available: [ ocaml-version >= "4.02.3"]
+homepage: "https://github.com/ocaml-community/yojson"
+bug-reports: "https://github.com/ocaml-community/yojson/issues"
+dev-repo: "git+https://github.com/ocaml-community/yojson.git"
+doc: "https://ocaml-community.github.io/yojson/"
 build: [
   ["jbuilder" "subst" "-n" name] {pinned}
   ["jbuilder" "build" "-p" name "-j" jobs]
 ]
-
-build-test: [
-  ["jbuilder" "runtest" "-p" name]
-]
-
+run-test: ["jbuilder" "runtest" "-p" name]
 depends: [
+  "ocaml" {>= "4.02.3"}
   "jbuilder" {build}
   "cppo" {build}
   "easy-format"
   "biniou" {>= "1.2.0"}
 ]
+synopsis:
+  "Yojson is an optimized parsing and printing library for the JSON format"
+description: """
+Yojson is an optimized parsing and printing library for the JSON format.
+
+It addresses a few shortcomings of json-wheel including 2x speedup,
+polymorphic variants and optional syntax for tuples and variants.
+
+ydump is a pretty-printing command-line program provided with the
+yojson package.
+
+The program atdgen can be used to derive OCaml-JSON serializers and
+deserializers from type definitions."""