This is just that I added a lot of comments to each new command in the CMakeList
file, because if I ever have to re-use this obscure and infrequently used skill,
I'll have a record written in my own words.
This matches the learning process that I describe in rigged_regex. Step by
step, recording everything multiple times and in multiple ways, so that all the
learning that I care about is preserved. There's XCB in here, and some C++
(mostly around `unique_ptr`).