switch to [slug].json.js server routes, instead of /api/...

routes/blog.json.js

@@ -0,0 +1,16 @@
+import posts from './blog/_posts.js';
+
+const contents = JSON.stringify(posts.map(post => {
+	return {
+		title: post.title,
+		slug: post.slug
+	};
+}));
+
+export function get(req, res) {
+	res.set({
+		'Content-Type': 'application/json'
+	});
+
+	res.end(contents);
+}