cleaned up indentation in tenpay.rb
modified expected result due to code change
Added implementation for wxpay (微信支付)
  * currently we are only targetting the follow scenario:
    * the ecommerce website creates an order
    * the site gets a payment url from wxpay website, with the order info
    * the site displays the payment url as a QRcode
    * the customer pull out his/her phone, opens "WeChat" and scans the QRcode
    * the customer pays within WeChat, using wxpay
    * the wxpay backend server notifies the ecommerce website that the order is paid
  * for this to work, you need to have an account on mp.weixin.qq.com that is authorized to receive wxpay
improved Wxpay implementation
added "orderquery" helper implementation to wxpay
refactored wxpay code to reduce redundant code in setting up all the fields in the requests/responses
added orderquery api response test case