Migrate external links page to Hugo

The external links are organized in individual, partial pages, which is
why this commit also adds the landing page that includes them (as
shortcodes because partials can only be used inside `layouts/`, not in
`content/`).

Signed-off-by: Victoria Dye <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: vdye

content/doc/ext/_index.html

@@ -0,0 +1,21 @@
+---
+section: "documentation"
+subsection: "external-links"
+title: "Git - External Links"
+url: /doc/ext.html
+aliases:
+- /doc/ext/index.html
+---
+
+<div id='main'>
+  <h1>External Links</h1>
+
+  {{< external/tutorials >}}
+
+  {{< external/books >}}
+
+  {{< external/videos >}}
+
+  {{< external/courses >}}
+
+</div>

app/views/doc/_ext_books.erb layouts/shortcodes/external/books.htmlapp/views/doc/_ext_books.erb renamed to layouts/shortcodes/external/books.html

@@ -78,7 +78,7 @@ <h4><a href="https://www.packtpub.com/web-development/learn-git-3-hours-video">L
         <p class='description'>
           Build powerful and effective projects using Git Version Control Systems.
         </p>
-      </li>      
+      </li>
       <li>
         <h4><a href="https://www.python4data.science/en/latest/productive/git/index.html">Git for Data Science</a></h4>
         <p class='description'>
@@ -124,7 +124,7 @@ <h4><a href="https://www.packtpub.com/web-development/git-and-version-control-vi
         <p class='description'>
           Learn the basics of Git and Version Control through detailed and easy to follow steps.
         </p>
-      </li>      
+      </li>
     </ul>
   </div>
 </div>