[FEATURE] Csrf token

- Added functionality to CsrfToken class.
- Added header support to Request class.
- Added option to set BaseCsrfVerifier class in RouterBase and
  SimpleRouter.

src/Pecee/Http/Middleware/Middleware.php

@@ -7,7 +7,5 @@ use Pecee\SimpleRouter\RouterEntry;
 
 abstract class Middleware
 {
-    public function handle(Request $request) {
-        return true;
-    }
+    abstract function handle(Request $request);
 }