casbin enhancement

Casbin is a powerful and efficient open-source access control library for Golang projects. It provides support for enforcing authorization based on various access control models. And it loads policy from persistent storage, all kinds of adapters are needed. So repository maintenance is quite important and complex. I will fix bugs which come from users using, explain user’s questions. For casbin itself, I will try my best to improve some methods’ performance and implement new features for it. For adapters, I’d like to maintain its dependency.