WIP: Adds typing to the decorators

[fabiob]

What do these changes do?

They add strong typing to aiocache decorator syntax.

Are there changes in behavior for the user?

Somewhat, as their IDEs will start to hint at the expected usage of the decorators.

Related issue number

It is related to #512 and #791

Checklist

• I think the code is well written (still a WIP though)
• Unit tests for the changes exist (would love to get some guidance on that)
• Documentation reflects the changes (I'm not sure it is needed)

[Dreamsorcerer]

Any typing improvements will need to wait until other tasks on the v1 milestone are complete. At the very least, we need mypy running, but that's currently blocked by 3 tasks preceding it: https://github.com/aio-libs/aiocache/milestone/8
(I ordered the tasks in the milestone so, for the most part, they need to be completed in that order to avoid issues).

[guybortnikov]

@fabiob @Dreamsorcerer any update on this PR? It will help for any project that uses type checking

[Dreamsorcerer]

See the previous comment: #838 (comment)