Allow setCacheFile method on router, Alias Slim's Router (#15)

* Alias Slim's Router, allow setCacheFile method

Add an alias so that Slim\Router => 'router' so you can  type hint the
Router in a controller.  Pass any settings for for routerCacheFile to
the setCacheFile method to enable FastRoute’s cache.

* Update minimum Slim requirements to 3.4.0

Allows routerCacheFile

Author: tflight

composer.json

@@ -17,7 +17,7 @@
         "php": "~5.5|~7.0",
         "php-di/php-di": "^5.2.0",
         "php-di/invoker": "^1.2.0",
-        "slim/slim": "^3.2.1"
+        "slim/slim": "^3.4.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.8"

src/config.php

@@ -35,7 +35,9 @@
     ],
 
     // Default Slim services
-    'router' => DI\object(Slim\Router::class),
+    'router' => DI\object(Slim\Router::class)
+        ->method('setCacheFile', DI\get('settings.routerCacheFile')),
+    Slim\Router::class => DI\get('router'),
     'errorHandler' => DI\object(Slim\Handlers\Error::class)
         ->constructor(DI\get('settings.displayErrorDetails')),
     'phpErrorHandler' => DI\object(Slim\Handlers\PhpError::class)