Added helper file with environment related functions.

application/helpers/env_helper.php

@@ -0,0 +1,37 @@
+<?php defined('BASEPATH') or exit('No direct script access allowed');
+
+/* ----------------------------------------------------------------------------
+ * Easy!Appointments - Open Source Web Scheduler
+ *
+ * @package     EasyAppointments
+ * @author      A.Tselegidis <alextselegidis@gmail.com>
+ * @copyright   Copyright (c) 2013 - 2020, Alex Tselegidis
+ * @license     http://opensource.org/licenses/GPL-3.0 - GPLv3
+ * @link        http://easyappointments.org
+ * @since       v1.1.0
+ * ---------------------------------------------------------------------------- */
+
+if ( ! function_exists('env'))
+{
+    /**
+     * Gets the value of an environment variable.
+     *
+     * Example:
+     *
+     * $debug = env('debug', FALSE);
+     *
+     * @param string $key
+     * @param mixed $default
+     *
+     * @return mixed
+     */
+    function env(string $key, $default = NULL)
+    {
+        if (empty($key))
+        {
+            throw new InvalidArgumentException('The $key argument cannot be empty.');
+        }
+
+        return $_ENV[$key] ?? $default;
+    }
+}