Handle delims in reference fields

Edge case that cropped up somewhere or other. Not sure if it's actually
correct to do this but it fixed a parse error so I'll live with it for
now.

src/Text/Pandoc/Readers/Mdoc.hs

@@ -1256,7 +1256,7 @@ referenceField :: PandocMonad m => T.Text -> ReferenceField -> MdocParser m ()
 referenceField m field = do
   macro m
   reference <- currentReference <$> getState
-  contents <- T.unwords <$> litsToText
+  contents <- stringify <$> litsAndDelimsToInlines
   eol
   modifyState $ \s -> s{currentReference = M.insertWith (++) field [contents] reference}
   return ()