fix: register plugin correctly

closes #54

Author: arnoson

example/site/plugins/kirby-vite/index.php

@@ -1,3 +1,3 @@
 <?php
 
-require dirname(__DIR__, 4) . '/packages/kirby-vite/index.php';
+require dirname(__DIR__, 4) . '/index.php';

index.php

@@ -1,3 +1,11 @@
-<?php
+<?php declare(strict_types=1);
 
-require __DIR__ . '/packages/kirby-vite/index.php';
+use arnoson\KirbyVite\Vite;
+
+require_once __DIR__ . '/packages/kirby-vite/Vite.php';
+
+Kirby\Cms\App::plugin('arnoson/kirby-vite', []);
+
+function vite() {
+  return Vite::getInstance();
+}