feh: add themes option (#6074)

- added themes option
- added themes test
- updated broken man page links

tests/modules/programs/feh/feh-themes.nix

@@ -0,0 +1,32 @@
+{ pkgs, ... }:
+
+{
+  config = {
+    programs.feh.enable = true;
+
+    programs.feh.themes = {
+      feh = [ "--image-bg" "black" ];
+      webcam = [ "--multiwindow" "--reload" "20" ];
+      present = [ "--full-screen" "--sort" "name" "--hide-pointer" ];
+      booth = [ "--full-screen" "--hide-pointer" "--slideshow-delay" "20" ];
+      imagemap = [
+        "-rVq"
+        "--thumb-width"
+        "40"
+        "--thumb-height"
+        "30"
+        "--index-info"
+        "%n\\n%wx%h"
+      ];
+      example = [ "--info" "foo bar" ];
+    };
+
+    test.stubs.feh = { };
+
+    nmt.script = ''
+      assertFileContent \
+        home-files/.config/feh/themes \
+        ${./feh-themes-expected}
+    '';
+  };
+}