# Functions
NewPay return an instance of Pay package.
# Structs
Base 公用参数.
Config 是传出用于 js sdk 用的参数.
NotifyResp 消息通知返回.
NotifyResult 下单回调.
Params was NEEDED when request unifiedorder 传入的参数，用于生成 prepay_id 的必需参数.
Pay struct extends context.
PreOrder 是 unifie order 接口的返回.
RefundParams 调用参数.
RefundResponse 接口返回.