Add posts and old grade-calc

Fix small bugs
>bad commit

util/post-cache.ts

@@ -0,0 +1,14 @@
+import fs from 'fs';
+import { getAllPosts } from '../lib/slug';
+import { join } from 'path';
+
+const publicDir = join(process.cwd(), 'public');
+
+export default function cachePostLinkData() {
+    const posts = getAllPosts(['title', 'slug', 'last_updated']);
+    fs.writeFile(`${publicDir}/posts.json`, JSON.stringify(posts), (e) => {
+        if (e)
+            console.error(e);
+    });
+    return posts;
+}