docs: what citefind reads, and a citation graph built out of the books

The README now lists the forms it handles with an example of each, says that
where the italics sit is what decides whether they are the title or the
journal, and sets out what it refuses and why — scripture, Migne, a
contributor's biography, a note that only thanks people, a page footer.

Recipes gains "What a book leans on": one bibliography read, then the same
over a shelf, counted per citing book so a work cited forty times in one
bibliography still counts once. Every command was run — thirty converted
books gave 14,481 references, 10,536 naming a work, in about a second.

`records.md` now points at the five tools whose record shapes live in their
own pages rather than in `corpus-core`.

And pandoc escapes an underscore, so the rule of them that stands in for a
repeated author arrives as `\_\_\_\_\_` and was not being recognised.

docs/records.md

@@ -111,6 +111,14 @@ has a shape of its own, described where that tool is:
   and the call that would do it.
 - [`pdfgutter`](../crates/pdfgutter/README.md) — whether a scan is two pages
   to a sheet, and what each sampled page measured.
+- [`citefind`](../crates/citefind/README.md) — one reference out of a
+  bibliography, and the fields it could not read off the entry.
+- [`bookmeta`](../crates/bookmeta/README.md) — what a file says about itself.
+- [`tocfind`](../crates/tocfind/README.md) — one entry of a table of contents.
+- [`seriesof`](../crates/seriesof/README.md) — what a title says about its
+  series.
+- [`idnorm`](../crates/idnorm/README.md) — an identifier as it arrived and as
+  it should be stored.
 
 ## Getting the schemas