python.pkgs.packaging: move to separate expression

pkgs/development/python-modules/packaging/default.nix

@@ -0,0 +1,24 @@
+{ stdenv, buildPythonPackage, fetchPypi
+, pyparsing, six, pytest, pretend }:
+
+buildPythonPackage rec {
+  pname = "packaging";
+  version = "16.8";
+  name = "${pname}-${version}";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "5d50835fdf0a7edf0b55e311b7c887786504efea1177abd7e69329a8e5ea619e";
+  };
+
+  propagatedBuildInputs = [ pyparsing six ];
+
+  buildInputs = [ pytest pretend ];
+
+  meta = with stdenv.lib; {
+    description = "Core utilities for Python packages";
+    homepage = "https://github.com/pypa/packaging";
+    license = [ licenses.bsd2 licenses.asl20 ];
+    maintainers = with maintainers; [ bennofs ];
+  };
+}