Move base overlays packages to a separate directory.

overlay.nix

@@ -1,6 +1,6 @@
 self: super:
 with import ./lib/mk-overlay.nix { inherit (super) lib; };
 applyOverlays self super [
-  (import ./base.nix)
+  (import ./pkgs)
   (import ./distros)
 ]

pkgs/bson/default.nix

@@ -0,0 +1,20 @@
+{ lib, buildPythonPackage, fetchPypi, dateutil }:
+
+buildPythonPackage rec {
+  pname = "bson";
+  version = "0.5.9";
+  
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "0n01axc6vnszmbz1mx64d2blrb78hbcvlnl4v4a5h39mzb8nv844";
+  };
+
+  propagatedBuildInputs = [ dateutil ];
+
+  meta = with lib; {
+    description = "Independent BSON codec for Python that doesn't depend on MongoDB.";
+    homepage = "https://github.com/py-bson/bson";
+    license = licenses.bsd3;
+    maintainers = with maintainers; [ lopsided98 ];
+  };
+}

pkgs/default.nix

@@ -2,6 +2,8 @@ self: super: with super.lib; let
 
   pythonOverridesFor = python: python.override (old: {
     packageOverrides = pySelf: pySuper: {
+      bson = pySelf.callPackage ./bson { };
+    
       catkin-pkg = pySelf.callPackage ./catkin-pkg { };
 
       colcon-cmake = pySelf.callPackage ./colcon/cmake.nix { };