Made the code more robust.

Extended functionality with helper functions.

src/functions.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Joop\Asynchronous;
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+if (!function_exists('async_run')) {
+
+	/**
+	 * @param callable $function
+	 * @param mixed ...$parameters
+	 * @return Promise|null
+	 */
+	function async(callable $function, ...$parameters)
+	{
+		return Asynchronous::run($function, ...$parameters);
+	}
+}
+
+
+if (!function_exists('async_cleanup')) {
+	/**
+	 *
+	 */
+	function async_cleanup()
+	{
+		Asynchronous::cleanup();
+	}
+}