add gin-stats middleware (#162)

@appleboy my bad closed old PR and create again.

README.md

@@ -40,3 +40,4 @@ Each author is responsible of maintaining his own code, although if you submit a
 + [gin-redis-ip-limiter](https://github.com/Salvatore-Giordano/gin-redis-ip-limiter) - Request limiter based on ip address. It works with redis and with a sliding-window mechanism.
 + [gin-method-override](https://github.com/bu/gin-method-override) - Method override by POST form param `_method`, inspired by Ruby's same name rack
 + [gin-access-limit](https://github.com/bu/gin-access-limit) - An access-control middleware by specifying allowed source CIDR notations.
++ [gin-stats](https://github.com/semihalev/gin-stats) - Lightweight and useful request metrics middleware