Emacspy compat

While working on the keyboard-quit feature, I realized that Python needs to run in a separate thread. That discovery led me to rewrite my entire fork in C, which unfortunately means losing the ability to call Emacs functions from Python. Because this is such a big change, I decided to rebrand my fork.

The merge request below contains the last version that still supports calling Emacs functions from Python. My earlier commits also enable this project to compile on a more up-to-date system, so those might be worth cherry-picking. Beyond that, I’m unsure if anything else in my fork would fit here.