Declare the package to be typed

[vojavocni]

At the moment, tools like mypy will ignore the type-hints that exist in the package.

To declare the package as typed, the py.typed marker can be added like here: https://github.com/aio-libs/aiohttp/blob/master/aiohttp/py.typed.

This will help a lot for us using the package in our code.

[Pringled]

Hi @vojavocni,

Thanks for raising this, this was indeed missing. I've just created a PR for this: #214.

We'll include this in the next release.