Add support for imenu-list package

Thanks to newhallroad for bringing this matter to my attention in
issue 35 on the GitHub mirror:
<#35>.

README.org

@@ -1358,6 +1358,7 @@ everything most users need.
 - hi-lock (=M-x highlight-regexp=)
 - ibuffer
 - image-dired
+- imenu-list [ Part of {{{development-version}}}. ]
 - info
 - isearch, occur, query-replace
 - jit-spell
@@ -1749,7 +1750,7 @@ matters.
   Daniel Mendler, Federico Stilman, Iris Garcia, Jean-Philippe Gagné
   Guay, Jonas Collberg, Saša Janiška, Spike-Leung, Steve Molitor,
   Summer Emacs, Sven Seebeck, Thanos Apollo, Zoltán Király, goldfita,
-  marasenna.
+  marasenna, newhallroad.
 
 * GNU Free Documentation License
 :PROPERTIES:

ef-themes.el

@@ -1518,6 +1518,15 @@ text should not be underlined as well) yet still blend in."
     `(image-dired-thumb-header-file-name ((,c :inherit bold)))
     `(image-dired-thumb-header-file-size ((,c :foreground ,info)))
     `(image-dired-thumb-mark ((,c :background ,info :box (:line-width -3))))
+;;;; imenu-list
+    `(imenu-list-entry-face-0 ((,c :foreground ,rainbow-0)))
+    `(imenu-list-entry-face-1 ((,c :foreground ,rainbow-1)))
+    `(imenu-list-entry-face-2 ((,c :foreground ,rainbow-2)))
+    `(imenu-list-entry-face-3 ((,c :foreground ,rainbow-3)))
+    `(imenu-list-entry-subalist-face-0 ((,c :inherit bold :foreground ,rainbow-4 :underline t)))
+    `(imenu-list-entry-subalist-face-1 ((,c :inherit bold :foreground ,rainbow-5 :underline t)))
+    `(imenu-list-entry-subalist-face-2 ((,c :inherit bold :foreground ,rainbow-6 :underline t)))
+    `(imenu-list-entry-subalist-face-3 ((,c :inherit bold :foreground ,rainbow-7 :underline t)))
 ;;;; info
     `(Info-quoted ((,c :inherit ef-themes-fixed-pitch :foreground ,prose-verbatim))) ; the capitalization is canonical
     `(info-header-node ((,c :inherit (shadow bold))))