Move list retrieve/render to class (#15)

- array_key_exists -> key_exists

src/public/feed/index.php

@@ -35,7 +35,7 @@ if ($_SERVER['REQUEST_METHOD'] == 'POST') {
         $toEdit = Feed::retrieveById($_POST['id'], $db);
         $result = $toEdit ? Feed::update($toEdit, $_POST['url'], $db) : ['error' => "Feed {$_POST['id']} not found"];
     }
-    if (array_key_exists('ok', $result)) {
+    if (key_exists('ok', $result)) {
         add_info('Feed saved successfully');
         frc_redirect('/feeds');
     }