Add function to generate machine option lists + use it for services.

fn.nix

@@ -69,4 +69,11 @@ rec {
           true)
     ))
     ld);
+  makeOptionTypeList = path: (lists.forEach
+    # get a list of all files ending in .nix in path
+    (filter (filePath: hasSuffix ".nix" filePath)
+      (lsfRec path true))
+    # remove leading path and trailing ".nix", replace every slash with "::"
+    (replaceStrings [ "${path}/" "/" ".nix" ] [ "" "::" "" ])
+  );
 }