Added custom lib (stolen from hlissner's dotifles)

lib/options.nix

@@ -0,0 +1,18 @@
+{ lib, ... }:
+
+let
+  inherit (lib) mkOption types;
+in
+rec {
+  mkOpt  = type: default:
+    mkOption { inherit type default; };
+
+  mkOpt' = type: default: description:
+    mkOption { inherit type default description; };
+
+  mkBoolOpt = default: mkOption {
+    inherit default;
+    type = types.bool;
+    example = true;
+  };
+}