Create a render ast node type.

src/intermediate/registry.rs

@@ -31,6 +31,13 @@ impl<'parse> Registry<'parse> {
         })
     }
 
+    pub(crate) fn get_footnote_ids(&self) -> impl Iterator<Item = (usize, &Vec<IAstNode>)> {
+        self.footnote_ids
+            .iter()
+            .map(|(_label, definition)| definition)
+            .enumerate()
+    }
+
     /// Get a 0-indexed ID for a footnote.
     ///
     /// This needs to be incremented to be 1-indexed for render.