add v5 system api

src/Api/OkexV5/System.php

@@ -0,0 +1,18 @@
+<?php
+namespace Lin\Okex\Api\OkexV5;
+
+use Lin\Okex\Request;
+
+class System extends Request{
+
+    /**
+     * GET /api/v5/system/status
+     * */
+    public function getStatus(array $data=[]){
+        $this->type='GET';
+        $this->path='/api/v5/system/status';
+
+        $this->data=$data;
+        return $this->exec();
+    }
+}

src/OkexV5.php

@@ -10,6 +10,7 @@
 use Lin\Okex\Api\OkexV5\Market;
 use Lin\Okex\Api\OkexV5\Publics;
 use Lin\Okex\Api\OkexV5\SubAccount;
+use Lin\Okex\Api\OkexV5\System;
 use Lin\Okex\Api\OkexV5\Trade;
 
 class OkexV5
@@ -93,4 +94,11 @@ public function subaccount(){
     public function trade(){
         return new Trade($this->init());
     }
+
+    /**
+     *
+     * */
+    public function system(){
+        return new System($this->init());
+    }
 }