Added clear-config-cache utility

Per conversation on zendframework#54, we want to make production settings the
default, which means enabling the configuration cache. However, we also
need to make it easy for developers to clear the configuration cache.

This patch adds a script, `bin/clear-config-cache.php`, which can be
used to remove the configured configuration cache file, if defined. It
is aliased in `composer.json` as `clear-config-cache`, allowing usage as
`composer clear-config-cache`.

bin/clear-config-cache.php

@@ -0,0 +1,46 @@
+<?php
+/**
+ * Script for clearing the configuration cache.
+ *
+ * Can also be invoked as `composer clear-config-cache`.
+ *
+ * @see       https://github.com/zendframework/zend-expressive-skeleton for the canonical source repository
+ * @copyright Copyright (c) 2017 Zend Technologies USA Inc. (http://www.zend.com)
+ * @license   https://github.com/zendframework/zend-expressive-skeleton/blob/master/LICENSE.md New BSD License
+ */
+
+chdir(__DIR__ . '/../');
+
+require 'vendor/autoload.php';
+
+$config = include 'config/config.php';
+
+if (! isset($config['config_cache_path'])) {
+    echo "No configuration cache path found" . PHP_EOL;
+    exit(0);
+}
+
+if (! file_exists($config['config_cache_path'])) {
+    printf(
+        "Configured config cache file '%s' not found%s",
+        $config['config_cache_path'],
+        PHP_EOL
+    );
+    exit(0);
+}
+
+if (false === unlink($config['config_cache_path'])) {
+    printf(
+        "Error removing config cache file '%s'%s",
+        $config['config_cache_path'],
+        PHP_EOL
+    );
+    exit(1);
+}
+
+printf(
+    "Removed configured config cache file '%s'%s",
+    $config['config_cache_path'],
+    PHP_EOL
+);
+exit(0);

composer.json

@@ -59,6 +59,7 @@
             "@cs-check",
             "@test"
         ],
+        "clear-config-cache": "php bin/clear-config-cache.php",
         "cs-check": "phpcs",
         "cs-fix": "phpcbf",
         "serve": "php -S 0.0.0.0:8080 -t public public/index.php",