Add zip_safe=False to setup.py

[Stannislav]

According to
https://mypy.readthedocs.io/en/latest/installed_packages.html#installed-packages

"If you use setuptools, you must pass the option zip_safe=False to setup(),
or mypy will not be able to find the installed package."

[Stannislav]

@FrancescoCasalegno sorry I'm late for reviewing #192 I just scrolled through the changes and then stumbled upon the note about zip_safe in the mypy documentation. What do you think?

[FrancescoCasalegno]

LGTM! Feel free to merge with master!

I am actually surprised to learn that mypy should not have been able to find our package, as in my environment it seemed to work fine.

[Stannislav]

Here are more details about why it's recommended to have zip_safe=False: python/mypy#8802

If I understand correctly, it's important only if one uses the (legacy) python setup.py install syntax instead of pip install ..