python-packages: separate `specific-versions` pkgs

This simplifies maintenance.

pkgs/python-packages/default.nix

@@ -11,14 +11,6 @@ in {
   urldecode = callPackage ./urldecode {};
   chromalog = callPackage ./chromalog {};
   txzmq = callPackage ./txzmq {};
-  recommonmark = callPackage ./recommonmark { inherit (super) recommonmark; };
-
-  # cryptography 3.3.2, required by joinmarketdaemon
-  cryptography = callPackage ./cryptography {};
-  cryptography_vectors = callPackage ./cryptography/vectors.nix {};
-
-  # twisted 20.3.0, required by joinmarketbase
-  twisted = callPackage ./twisted {};
 
   joinmarketbase = joinmarketPkg ./jmbase;
   joinmarketclient = joinmarketPkg ./jmclient;
@@ -28,4 +20,16 @@ in {
   pyln-client = clightningPkg ./pyln-client;
   pyln-proto = clightningPkg ./pyln-proto;
   pylightning = clightningPkg ./pylightning;
+
+  ## Specific versions of packages that already exist in nixpkgs
+
+  # cryptography 3.3.2, required by joinmarketdaemon
+  cryptography = callPackage ./specific-versions/cryptography {};
+  cryptography_vectors = callPackage ./specific-versions/cryptography/vectors.nix {};
+
+  # twisted 20.3.0, required by joinmarketbase
+  twisted = callPackage ./specific-versions/twisted.nix {};
+
+  # recommonmark 0.7.1, required by pyln-client
+  recommonmark = callPackage ./specific-versions/recommonmark.nix { inherit (super) recommonmark; };
 }