prebuild wheels code

[benblack769]

Hi, I really like your library and would like to use it as a dependency of our library.

The only thing stopping us from depending on this tool is that requiring users to install libjpeg and libpng is untenable, as not all users have admin privileges.

The solution for this is having comprehensive pre-built wheels.

This PR has some useful code to make github actions make pre-built wheels for various systems for you. All you need to do is:

1. Set up github Secrets so that the ${{ secrets.PYPI_USER }} and ${{ secrets.PYPI_PASSWORD }} work correctly.
2. Create a production branch and push to it when making a new release.

Let me know what you think.