Use macros for creating the intermediate stage.

This is to make it easier to change function signatures by consolidating the places where the signatures exist.

src/intermediate/footnote_reference.rs

@@ -1,6 +1,6 @@
-use crate::error::CustomError;
-
+use super::macros::intermediate;
 use super::registry::Registry;
+use crate::error::CustomError;
 
 #[derive(Debug, Clone)]
 pub(crate) struct IFootnoteReference {
@@ -8,11 +8,10 @@ pub(crate) struct IFootnoteReference {
     duplicate_offset: usize,
 }
 
-impl IFootnoteReference {
-    pub(crate) async fn new<'b, 'parse>(
-        registry: &'b mut Registry<'parse>,
-        original: &'b organic::types::FootnoteReference<'parse>,
-    ) -> Result<IFootnoteReference, CustomError> {
+intermediate!(
+    IFootnoteReference,
+    FootnoteReference,
+    |registry, original| async {
         let footnote_id = registry
             .get_footnote_reference_id(original.label, &original.definition)
             .await?;
@@ -21,7 +20,9 @@ impl IFootnoteReference {
             duplicate_offset: 0, // TODO
         })
     }
+);
 
+impl IFootnoteReference {
     pub(crate) fn get_display_label(&self) -> String {
         format!("{}", self.footnote_id + 1)
     }