versions: bump to 20.09 and improve NIX_PATH assembly

The NIX_PATH assembly now walks over all keys in the given channel
repositories and assembles a NIX_PATH entry from it. Previously it made
assumptions about a set of hardcoded keys being available, which wasn't
ideal as it didn't allow device-entries.

nix/pkgs/default.nix

@@ -66,4 +66,28 @@ in rec {
   duplicacy = pkgs.callPackage ../pkgs/duplicacy {};
   mfcl3770cdw = pkgs.callPackage ../pkgs/mfcl3770cdw.nix {};
   staruml = pkgs.callPackage ../pkgs/staruml.nix { inherit (pkgs.gnome2) GConf; libgcrypt = pkgs.libgcrypt_1_5; };
+
+  myPython = pkgs.python37Full.withPackages (ps: with ps; [
+    pep8 yapf flake8
+    # autopep8 (broken)
+    # pylint (broken)
+    ipython
+    llfuse
+    dugong
+    defusedxml
+    wheel
+    pip
+    virtualenv
+    cffi
+    pyopenssl
+    urllib3
+    mistune
+
+    flask
+
+    pyaml
+  ] ++ [
+    pkgs.pypi2nix
+    pkgs.libffi
+  ]);
 }