ATX heading-like construct in list item is treated as heading

[uranusjr]

Example:

* Foo
* # Bar

# Bar will be highlighted as heading.

[ali-rantakari]

This might seem unintuitive, but it's how peg-markdown handles it as well:

$ peg-markdown example.md 
<ul>
<li>Foo</li>
<li><h1>Bar</h1></li>
</ul>