add chapter about data repositories, and start work on perfomance chapter

implementation/15-adding-content/config/middlewares.php

@@ -0,0 +1,11 @@
+<?php declare(strict_types=1);
+
+use Lubian\NoFramework\Http\RouteMiddleware;
+use Middlewares\TrailingSlash;
+use Middlewares\Whoops;
+
+return [
+    Whoops::class,
+    TrailingSlash::class,
+    RouteMiddleware::class,
+];