Allow to have middleware for the path same with a HTML page

HTTP allows to change the type of the content to serve by Accept field in
the request. The middleware for the path same with a HTML page will
be inserted before the HTML renderer, and can take advantage of this
feature, using expressjs's "accepts" method, for example.

src/interfaces.ts

@@ -1,7 +1,9 @@
 export type Route = {
 	id: string;
-	type: 'page' | 'route';
-	file: string;
+	handlers: {
+		type: 'page' | 'route';
+		file: string;
+	}[];
 	pattern: RegExp;
 	test: (url: string) => boolean;
 	exec: (url: string) => Record<string, string>;