make_index.py — the program that built appendix I

It reads the rendered pdf of the book, counts how often each term of its own
list appears on each page, keeps the pages where the term is the subject rather
than a passing mention, reads the printed page number off the foot of each page,
and writes index_data.py, which the book's build script renders.

Then it checks itself: it goes back through the pages and looks for every term
on every page the index sends you to.  The last line it prints is how many
references it made and how many of them were wrong.

    python3 make_index.py -v

It is here because an index is a claim about a book, and a claim in this book
is something you can check.
