[FEATURE] Bugfixes and optimisations

- Changed Middleware to interface - as it's easier to inherit and use in
  other frameworks/projects.

- RouterController now loads method based on request-method.

- Changed references to old Middleware abstract class.

- Middleware must now be instance of IMiddleware instead of Middleware
  class.

src/Pecee/Http/Middleware/IMiddleware.php

@@ -0,0 +1,8 @@
+<?php
+namespace Pecee\Http\Middleware;
+
+use Pecee\Http\Request;
+
+interface IMiddleware {
+    public function handle(Request $request);
+}