Allow positional args to be Choice<'a, 'a> to indicate whether they came before any positional marker (#238)

ConsumePlugin/Args.fs

@@ -128,3 +128,10 @@ type ParentRecordSelfPos =
         [<PositionalArgs>]
         AndAnother : bool list
     }
+
+[<ArgParser true>]
+type ChoicePositionals =
+    {
+        [<PositionalArgs>]
+        Args : Choice<string, string> list
+    }