Add py.typed

[vnmabus]

Is your feature request related to a problem? Please describe.
In order for Mypy to use the typing information of this project, you need to include a blank file called py.typed along the code, to comply with PEP 561 (https://www.python.org/dev/peps/pep-0561/). Otherwise Mypy skips this library in the type analysis.

Describe the solution you'd like
Add a blank py.typed file and package it along the code.

[ppizarror]

Hi. Can you create a new PR? Does setup.py file must be updated?

[vnmabus]

No, you don't need to add anything to setup.py, but the file must be in the MANIFEST.in in order for it to be packaged.

[ppizarror]

Uploaded to pip!

[vnmabus]

I can confirm that now it works!