Record the list item indent depth in the context tree.

src/parser/util.rs

@@ -9,6 +9,7 @@ pub fn in_section<'r, 's, 'x>(context: Context<'r, 's>, section_name: &'x str) -
             ContextElement::Context(name) if *name == section_name => return true,
             ContextElement::Context(_) => {}
             ContextElement::StartOfParagraph => {} // TODO: If we specialize this to bold then this would be a good spot to stop scanning
+            ContextElement::ListItem(_) => {}
         }
     }
     false