Example repo for a cython package that cimports h3-py

[ajfriend]

I think it would be helpful to provide a demo repository for setting up a Python package that cimports the Cython bits of h3-py. We have an example of doing this for a single file in https://github.com/uber/h3-py/blob/master/tests/test_cython/cython_example.pyx

Having an example for a package would help users who want to write fast Cython code with h3 functions outside of the main h3-py repo.

[ajfriend]

It would be nice to have a "modern" build as well: pyproject.toml and maybe something along the lines of https://learn.scientific-python.org/development/guides/packaging-compiled/

[ajfriend]

I made a sloppy first attempt here: https://github.com/ajfriend/h3_example_package