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/export_snippet.rs

@@ -27,7 +27,7 @@ pub fn export_snippet<'r, 's>(
     let (remaining, backend_name) = backend(context, remaining)?;
     let parser_context =
         context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
-            class: ExitClass::Beta,
+            class: ExitClass::Gamma,
             exit_matcher: &export_snippet_end,
         }));
     let (remaining, backend_contents) = opt(tuple((