Migrate build to pyproject.toml

[Technologicat]

The migration seems more complex than necessary. Waiting until someone writes an ELI5 migration guide.

An added point of complexity here is that we need to build the wheels either a) without compiling bytecode, or b) with macro-enabled bytecode, which requires a custom build command. And running custom commands in the installer is frowned upon (mostly for good reason, but here such a feature would be useful).

Seems we're not the only one in this boat, though.

You are telling me that we had a working python setup.py solution for 10+ years, this workflow is now quasi deprecated, and the recommended replacement is it's complicated?! I'm just trying to get my package modernized. Why does that need to be complicated?
--Gregory Szorc