lib: add evalSubmodule

lib/default.nix

@@ -10,6 +10,15 @@ let
 
     evalSource = import ./eval-source.nix;
 
+    evalSubmodule = submodule: modules: let
+      prefix = ["evalSubmodule"];
+    in evalModulesConfig [
+      {
+        options = removeAttrs (submodule.getSubOptions prefix) ["_module"];
+        imports = modules;
+      }
+    ];
+
     git = import ./git.nix { inherit lib; };
     haskell = import ./haskell.nix { inherit lib; };
     krebs = import ./krebs lib;