Headings should be in HTML-syntax if they contain block-elements

[EvitanRelta]

This HTML:

<h1>
<pre><code>Codeblock (a block-element)
</code></pre>
</h1>

<h1>
  <blockquote>Blockquote (another block-element)</blockquote>
<h1>

---

Cannot be represented in markdown. The below markdowns will not work:
Fenced-codeblock style: (current implementation's output)

# ```
Codeblock (a block-element)
```

# > Blockquote (another block-element)

Indented-codeblock style:

#     Codeblock (a block-element)

# > Blockquote (another block-element)

---

The correct conversion should be fully in HTML-syntax:

<h1>
<pre><code>Codeblock (a block-element)
</code></pre>
</h1>

<h1>
  <blockquote>Blockquote (another block-element)</blockquote>
</h1>

[EvitanRelta]

Fixed by the merge commi: cd1963d