html: Improve block rendering

org/testdata/example.html

@@ -23,7 +23,9 @@
 <li><p>unordered list item 3 - and a <a href="https://example.com">link</a> and some lines of text</p>
 <ol>
 <li><p>and another subitem</p>
-<code>echo with a block</code>
+<code class="src src-sh">
+<pre>echo with a block<pre>
+</code>
 </li>
 <li><p>and another one with a table</p>
 <table>
@@ -62,6 +64,21 @@
 </ol>
 </li>
 </ul>
+<h2>blocks</h2>
+<code class="src src-bash">
+<pre>echo a bash source block<pre>
+</code>
+<code class="src src-text">
+<pre>a source block without a language
+and a second line
+and a third one<pre>
+</code>
+<pre class="example">
+an example blockwith multiple lines
+</pre>
+<blockquote>
+Mongodb is very webscale
+</blockquote>
 <h2>Footnotes</h2>
 <ul>
 <li>normal footnote reference <sup class="footnote-reference"><a href="#footnote-1">1</a></sup></li>