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/page.rs

@@ -21,9 +21,10 @@ pub(crate) struct BlogPostPage {
 }
 
 impl BlogPostPage {
-    pub(crate) async fn new<'b, 'parse, P: Into<PathBuf>>(
+    // TODO: Move path into the registry so I can give this a standard interface like the others.
+    pub(crate) async fn new<'a, 'b, 'parse, P: Into<PathBuf>>(
         path: P,
-        registry: &'b mut Registry<'parse>,
+        registry: &'a mut Registry<'b, 'parse>,
         document: &'b organic::types::Document<'parse>,
     ) -> Result<BlogPostPage, CustomError> {
         let path = path.into();