org-hugo-slug: Convert "+" chars in headings to " plus "

ox-hugo.el

@@ -1805,7 +1805,8 @@ The `slug' generated from that STR follows these rules:
 - Not have *any* HTML tag like \"<code>..</code>\",
   \"<span class=..>..</span>\", etc.
 - Not contain any URLs (if STR happens to be a Markdown link).
-- Replace \".\" in STR with \"dot\", and \"&\" with \"and\".
+- Replace \".\" in STR with \"dot\", \"&\" with \"and\",
+  \"+\" with \"plus\".
 - Replace parentheses with double-hyphens.  So \"foo (bar) baz\"
   becomes \"foo--bar--baz\".
 - Replace non [[:alnum:]-] chars with spaces, and then one or
@@ -1820,10 +1821,14 @@ The `slug' generated from that STR follows these rules:
          ;; below regexp is the closing parenthesis of a Markdown
          ;; link: [Desc](Link).
          (str (replace-regexp-in-string (concat "\\](" ffap-url-regexp "[^)]+)") "]" str))
-         ;; Replace "&" with " and ".
-         (str (replace-regexp-in-string "&" " and " str))
-         ;; Replace "." with " dot ".
-         (str (replace-regexp-in-string "\\." " dot " str))
+         ;; Replace "&" with " and ", "." with " dot ", "+" with
+         ;; " plus ".
+         (str (replace-regexp-in-string
+               "&" " and "
+               (replace-regexp-in-string
+                "\\." " dot "
+                (replace-regexp-in-string
+                 "\\+" " plus " str))))
          ;; Replace all characters except alphabets, numbers and
          ;; parentheses with spaces.
          (str (replace-regexp-in-string "[^[:alnum:]()]" " " str))

test/site/content-org/all-posts.org

@@ -402,6 +402,10 @@ Something 2.1
 ** Releasing version 1.1
 ** Foo ( Bar ) Baz
 ** (Foo)Bar.Baz&Zoo
+- ~.~ → ~dot~
+- ~&~ → ~and~
+** C++
+- ~+~ → ~plus~
 ** Hey! I have a link [[https://example.org][here]] (Awesome!)
 ** Este título es en español
 ** Non-English titles

test/site/content/posts/post-heading-slugs.md

@@ -12,6 +12,14 @@ draft = false
 
 ## (Foo)Bar.Baz&Zoo {#foo--bar-dot-baz-and-zoo}
 
+-   `.` → `dot`
+-   `&` → `and`
+
+
+## C++ {#c-plus-plus}
+
+-   `+` → `plus`
+
 
 ## Hey! I have a link [here](https://example.org) (Awesome!) {#hey-i-have-a-link-here--awesome}