Create py.typed (#12893)
* Create py.typed
This creates a [py.typed as per PEP 561](https://www.python.org/dev/peps/pep-0561/#packaging-type-information) that should be distributed to mark that the package includes (inline) type annotations.
* Update setup.py
Include py.typed as package data
* Update setup.py
Call `setup(...)` with `zip_safe=False`.