Add a macro for calling parsers that take in the affiliated keywords.

src/parser/plain_list.rs

@@ -91,7 +91,7 @@ pub(crate) fn new_plain_list<'b, 'g, 'r, 's, AK>(
     input: OrgSource<'s>,
 ) -> Res<OrgSource<'s>, PlainList<'s>>
 where
-    AK: Iterator<Item = Keyword<'s>>,
+    AK: IntoIterator<Item = Keyword<'s>>,
 {
     todo!()
 }