nghttp2: add python bindings as pythonPackages.nghttp2

it's tricky to enable in nghttp2's default build, however, because it needs
to be usable by curl, a very core nix package, and we get cyclical
dependencies if we add python to its requirements. having it available as
a separate build is better than nothing, though.

pkgs/top-level/python-packages.nix

@@ -4533,6 +4533,12 @@ in {
 
   nevow = callPackage ../development/python-modules/nevow { };
 
+  nghttp2 = (toPythonModule (pkgs.nghttp2.override {
+    inherit (self) python cython setuptools;
+    inherit (pkgs) ncurses;
+    enablePython = true;
+  })).python;
+
   nibabel = callPackage ../development/python-modules/nibabel {};
 
   nidaqmx = callPackage ../development/python-modules/nidaqmx { };