Move objects to a lower exit class.

Paragraph's exit matcher which detects elements was causing the plain list parser to exit after the first item was parsed which was causing significant amounts of re-parsing.

src/parser/parser_context.rs

@@ -62,7 +62,7 @@ impl<'r, 's> ContextTree<'r, 's> {
         //         exit_matcher: ChainBehavior::IgnoreParent(Some(&always_fail)),
         //     }));
 
-        let mut current_class_filter = ExitClass::Beta;
+        let mut current_class_filter = ExitClass::Gamma;
         for current_node in self.iter() {
             let context_element = current_node.get_data();
             match context_element {