Add support for automatically building wheels on Linux and Mac

[dfm]

This PR adds a GitHub actions workflow that uses cibuildwheel to automatically build binary wheels for the standard Linux and Mac platforms. These wheels could be uploaded to PyPI manually or uploaded automatically (this is what I do with most of my projects). This would help with issues like #298 (because it packages all of the dependencies) and generally speed up pip-based dependency workflows, but some users might prefer to tune their cfitsio, and it adds some developer overhead, so you should definitely feel free to veto/ignore/etc.!

Also, I'll be happy to squash/rebase to clean up the history if this is something that you're interested in merging.

[beckermr]

I don't personally want to maintain this, but I'll leave the final say to @esheldon.

[esheldon]

Thanks @dfm

I don't know anything about wheels. I certainly could not maintain this.

How does this affect publishing to pypi or conda forge?

[dfm]

@esheldon, @beckermr: Thanks - I would find this a useful feature since I mostly use pip to manage my dependencies rather than conda, but I don't want to add extra maintenance burden! I think probably the best bet is to just close this if you aren't feeling comfortable with such a feature. Thanks for the consideration!

@esheldon: to answer your questions: I use a workflow like this to automatically publish to PyPI (both source and binary builds) on a tagged GitHub release (for example). It would not have any affect on conda/conda-forge whatsoever.