add support for markdown-it

examples/markdown/index.html

@@ -47,6 +47,8 @@
 # Markdown.js
 
 * Provided by [Markdown.js](https://github.com/evilstreak/markdown-js) in [extras/](https://github.com/impress/impress.js/tree/master/extras)
+* [markdown-it](https://github.com/markdown-it/markdown-it) and [marked](https://github.com/markedjs/marked)
+  is also supported
 * Jot down your bullet points in *Markdown* & have it automatically converted to HTML
 * Note: The Markdown is converted into a presentation client side, in the browser. This is unlike
   existing tools like [Hovercraft](https://github.com/regebro/hovercraft) and 
@@ -183,6 +185,7 @@ <h1>CSS &amp; JavaScript magic</h1>
 <script type="text/javascript" src="../../extras/mermaid/mermaid.min.js"></script>
 <script type="text/javascript" src="../../extras/markdown/markdown.js"></script>
 <!-- <script src="https://cdn.jsdelivr.net/npm/marked/marked.min.js"></script> -->
+<!-- <script src="https://cdnjs.cloudflare.com/ajax/libs/markdown-it/13.0.1/markdown-it.min.js"></script> -->
 
 <!--
     To make all described above really work, you need to include impress.js in the page.

js/impress.js

@@ -2041,6 +2041,13 @@
             return function( elem, src ) {
                 return marked.parse( src );
             };
+        } else if ( window.hasOwnProperty( "markdownit" ) ) {
+
+            // Using markdown-it
+            var md = markdownit();
+            return function( elem, src ) {
+                return md.render( src );
+            };
         } else if ( window.hasOwnProperty( "markdown" ) ) {
 
             // Using builtin markdown engine

src/plugins/extras/extras.js

@@ -27,6 +27,13 @@
             return function( elem, src ) {
                 return marked.parse( src );
             };
+        } else if ( window.hasOwnProperty( "markdownit" ) ) {
+
+            // Using markdown-it
+            var md = markdownit();
+            return function( elem, src ) {
+                return md.render( src );
+            };
         } else if ( window.hasOwnProperty( "markdown" ) ) {
 
             // Using builtin markdown engine