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/exiting.rs

@@ -8,6 +8,9 @@ pub enum ExitClass {
 
     /// Elements who cede priority to alpha elements when matching.
     Beta = 300,
+
+    /// Elements who cede priority to alpha and beta elements when matching.
+    Gamma = 4000,
 }
 
 impl std::fmt::Display for ExitClass {