Support list items with empty first line

also dismiss implementing ordered list bullet overrides for now, e.g.
1. [@10] foo

add it once someone needs it - for now it seems like needless complexity

org/testdata/lists.html

@@ -6,6 +6,12 @@ unordered list item 1
 </li>
 <li>
 <p>
+list item with empty first and second line <br>
+normally an empty line breaks the list item - but we make an exception for the first line and don&#39;t count it towards that limit
+</p>
+</li>
+<li>
+<p>
 unordered list item 2 - with <code>inline</code> <em>markup</em>
 </p>
 <ol>
@@ -36,6 +42,11 @@ ordered sublist item 3
 ordered sublist item 2
 </p>
 </li>
+<li>
+<p>
+list item with empty first and second line - see above
+</p>
+</li>
 </ol>
 </li>
 <li class="checked">