Update Markdown formatter to support footnotes and hard wraps natively

tests/_data/formatter/markdownextra.target2.html

@@ -0,0 +1,24 @@
+<div>
+
+<pre><code>This is *true* markdown text.
+</code></pre>
+
+</div>
+
+<p>This sentence has a footnote. <sup id="user_content_fnref:user_content_1"><a href="#fn:user_content_1" class="footnote-ref">1</a></sup></p>
+
+<pre><code>fenced code block
+</code></pre>
+
+<table><thead><tr><th>Hello</th>
+  <th>World</th>
+</tr></thead><tbody><tr><td>Foo</td>
+  <td>Bar</td>
+</tr><tr><td>Baz</td>
+  <td>Rhymix</td>
+</tr></tbody></table><div>
+<hr /><ol><li id="user_content_fn:user_content_1">
+<p>Here's the footnote content. <a href="#fnref:user_content_1" class="footnote-backref">↩︎</a></p>
+</li>
+
+</ol></div>