This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
sphinx expects that the description for a command (as appearing in its man
page) be provided in conf.py, not in the rst file itself. LLVM handles this
with some custom Python code that parses it out of the file. Do the same
thing in fish.