Add type marker for PEP 561

[trickeydan]

This indicates to type checker tools that typesystem has inline type hints.

Mypy is unable to tell otherwise, and errors, e.g:

inv/asset.py:3: error: Cannot find module named 'typesystem'
inv/asset.py:3: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
inv/asset.py:6: error: Class cannot subclass 'Schema' (has type 'Any')
inv/asset.py:6: error: Base type Schema becomes "Any" due to an unfollowed import
inv/asset.py:14: error: Expression has type "Any"
inv/asset.py:15: error: Expression has type "Any"
inv/asset.py:16: error: Expression has type "Any"
make: *** [Makefile:12: type] Error 1

More information on this can be found at https://www.python.org/dev/peps/pep-0561/#id18

[shamrin]

I think you also need to add zip_safe=False to setup.py.

See encode/databases#100 and encode/starlette#455.

[tomchristie]

Would probably prefer just a blank py.typed, in-line with encode/databases#100 and encode/starlette#455.

[trickeydan]

Fixed

[trickeydan]

I think you also need to add zip_safe=False to setup.py.

See encode/databases#100 and encode/starlette#455.

Fixed

[tomchristie]

Thanks!