hugo: replace threedash menu separator with css

This makes the menu separator a stylistic element and reduces the need
for a custom hugo-menu template to skip treating the menu element as a
link item. This helps to reduce future incompatibility by minimizing
overwritten templates.

Author: anthraxx

website/assets/_custom.scss

@@ -0,0 +1,5 @@
+nav>ul:last-of-type>li:last-child::before {
+  content: "⸻";
+  display: inline-block;
+  margin: 0.5em 0;
+}

website/config.toml

@@ -7,15 +7,6 @@ theme = "hugo-book"
   name = "⬅️  Back to top"
   url = "https://uapi-group.org/"
   weight = 1
-[[menu.before]]
-  name = "⸻"
-  weight = 2
-
-# Uncomment to show second separator after more content files were added
-#
-#[[menu.after]]
-#  name = "⸻"
-#  weight = 10
 
 [[menu.after]]
   name = "Collaborate on Github"