Switch wapi tradeFee to sapi commissionFee

As per #363 WAPI endpoints will disappear on Aug 1.
The old tradeFee function remains available until Binance decommissions it, but a deprecated warning is sent.
The new commissionFee function allows now calling it without argument, showing the full list of all symbols with the fees.

Author: ePascalC

php-binance-api.php

@@ -693,9 +693,31 @@ public function tradeFee(string $symbol)
             "symbol" => $symbol,
             "wapi" => true,
         ];
+        trigger_error('Function tradeFee is deprecated and will be removed from Binance on Aug 1, 2021. Please use $api->commissionFee', E_USER_NOTICE);
 
         return $this->httpRequest("v3/tradeFee.html", 'GET', $params, true);
     }
+    
+    /**
+     * commissionFee - Fetch commission trade fee
+     * 
+     * @link https://binance-docs.github.io/apidocs/spot/en/#trade-fee-user_data
+     * 
+     * @property int $weight 1
+     * 
+     * @param string $symbol  (optional)  Should be a symbol, e.g. BNBUSDT or empty to get the full list
+     * 
+     * @return array containing the response
+     * @throws \Exception
+     */    
+    public function commissionFee($symbol = '')
+    {
+        $params = array('sapi' => true);
+        if ($symbol != '' && gettype($symbol) == 'string')
+            $params['symbol'] = $symbol;
+
+        return $this->httpRequest("v1/asset/tradeFee", 'GET', $params, true);
+    }
 
     /**
      * withdraw requests a asset be withdrawn from binance to another wallet