Fix list parsing & ensure line breaks inside lists are handled correctly

- Break list when kind of bullet changes
- Ensure we render multiline list items correctly

org/testdata/example.html

@@ -253,6 +253,38 @@ either <code>this</code> or <code>that</code> foo.
 either <code>this</code>
 or <code>that</code> foo.
 </p>
+<h3><a href="https://github.com/chaseadamsio/goorgeous/issues/50">#50</a>: Linebreaks in lists are preserved</h3>
+<ul>
+<li>
+<p>
+this list item
+has
+multiple
+linbreaks - but it&#39;s still just one paragraph (i.e. no line breaks are rendered)
+</p>
+</li>
+<li>
+<p>
+foobar
+</p>
+</li>
+</ul>
+<ol>
+<li>
+<p>
+same
+goes
+for
+ordered
+lists
+</p>
+</li>
+<li>
+<p>
+foo
+</p>
+</li>
+</ol>
 <h3><a href="https://github.com/chaseadamsio/goorgeous/issues/68">#68</a>: Quote block with inline markup</h3>
 <blockquote>
 <p>