初始化项目：添加后端代码、ThinkPHP框架、前端资源

extend/Yansongda/Pay/Exceptions/GatewayException.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Yansongda\Pay\Exceptions;
+
+class GatewayException extends Exception
+{
+    /**
+     * Bootstrap.
+     *
+     * @author yansongda <me@yansonga.cn>
+     *
+     * @param string       $message
+     * @param array|string $raw
+     * @param int          $code
+     */
+    public function __construct($message, $raw = [], $code = self::ERROR_GATEWAY)
+    {
+        parent::__construct('ERROR_GATEWAY: '.$message, $raw, $code);
+    }
+}