added typing to function arguments and return types to pass linting c…

[joeygrable94]

Hello Friend,

I am using this library as inspiration for an API with fine-grained resource access control. I love the foundation you built here, but I keep running mypy linting and it throws the error message "missing library stubs or py.typed marker". In order to fix this problem I forked your repo, added typing to the function arguments and return types, then requested you merge this PR.

All the best,