fix: strip dots (and other chars) in fragment id of markdown links (#7029)

* fix bad link syntax in CONTRIBUTING-vi

* also dots, while we're at it

* also dots, while we're at it (remaining)

Recover changes and resolves suggestions made in https://github.com/EbookFoundation/free-programming-books/pull/7010#discussion_r947625933

* fix: strip ampersands `&` from fragment ids

* fix: strips other characters like `&`, `/`, `+`, `#`... to be compilant with Kramdown GMF processor

Co-authored-by: eric <eric@hellman.net>

courses/free-courses-ko.md

@@ -1,10 +1,10 @@
 ### Index
 
-* [Algorithms & Data Structures](#algorithms-&-data-structures)
+* [Algorithms & Data Structures](#algorithms--data-structures)
 * [Android](#android)
 * [Arduino](#arduino)
-* [ASP.NET](#asp.net)
-* [C/C++](#c/c++)
+* [ASP.NET](#aspnet)
+* [C/C++](#cc)
 * [C#](#csharp)
 * [Circuit](#circuit)
 * [Deep Learning](#deep-learning)
@@ -17,8 +17,8 @@
 * [Java](#java)
 * [JavaScript](#javascript)
     * [AngularJS](#angularjs)
-    * [Node.js](#node.js)
-    * [React.js](#react.js)
+    * [Node.js](#nodejs)
+    * [React.js](#reactjs)
 * [Kotlin](#kotlin)
 * [Linux](#linux)
 * [Machine Learning](#machine-learning)