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

src/parser/macros.rs

@@ -1 +1,25 @@
+/// Parse an element that has affiliated keywords.
+macro_rules! ak_element {
+    ($parser:ident, $affiliated_keywords:expr, $post_affiliated_keywords_input: expr, $context: expr, $input: expr, $wrapper: expr) => {
+        if let Ok((remaining, ele)) = $parser(
+            $affiliated_keywords,
+            $post_affiliated_keywords_input,
+            $context,
+            $input,
+        ) {
+            return Ok((remaining, $wrapper(ele)));
+        }
+    };
+    ($parser:ident, $affiliated_keywords:expr, $post_affiliated_keywords_input: expr, $context: expr, $input: expr) => {
+        if let Ok((remaining, ele)) = $parser(
+            $affiliated_keywords,
+            $post_affiliated_keywords_input,
+            $context,
+            $input,
+        ) {
+            return Ok((remaining, ele));
+        }
+    };
+}
 
+pub(crate) use ak_element;