Add auto links: Try to render unmarked urls as links

org/testdata/example.html

@@ -58,6 +58,7 @@
 <li>regular link <a href="https://example.com">https://example.com</a> link without description</li>
 <li>regular link <a href="https://example.com">example.com</a> link with description</li>
 <li>regular link to a file (image) <img src="my-img.png" alt="file:my-img.png" title="file:my-img.png" /></li>
+<li>auto link, i.e. not inside <code class="verbatim">\[[square brackets]\]</code> <a href="https://www.example.com">https://www.example.com</a></li>
 </ol>
 </li>
 </ul>

org/testdata/example.org

@@ -50,6 +50,7 @@ this one is cheating a little as tags are ALWAYS printed right aligned to a give
   1. regular link [[https://example.com]] link without description
   2. regular link [[https://example.com][example.com]] link with description
   3. regular link to a file (image) [[file:my-img.png]]
+  4. auto link, i.e. not inside =\[[square brackets]\]= https://www.example.com
 ** Footnotes
 - normal footnote reference [fn:1]
 - further references to the same footnote should not [fn:1] render duplicates in the footnote list