Typing

Since `aiocache` only supports modern Python 3 versions, I was wondering if there would be an interesting in having the library be typed?

I wouldn't mind doing the work to get this done, but wanted to get feedback on whether this is something that the maintainers of `aiocache` would even want.

On that same note, how do people feel about dropping Python 3.5 support now that the release has officially reached end-of-life.