format note content when creating slide

[jetzhliu]

In html content, marked allow Inline-Level Grammar but not Block-Level Grammar, so when I write following:

note:
* a
* b
* c

it become:

<p><em> a
</em> b</p>
<ul>
<li>c</li>
</ul>

unbelievable!

[hakimel]

Thanks. Your commit has been merged into the dev branch and will go out with the next release.