Fix Router and finish base view system.

src/Exceptions/InvalidViewException.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace App\Exceptions;
+use Throwable;
+
+class InvalidViewException extends \Exception {
+
+    public function __construct( string $viewName )
+    {
+        parent::__construct( "View {$viewName} does not exist.", 500 );
+    }
+
+}