Title casing

This was raised in #355 and is related to #160.

Do we have a policy for how to record the casing of titles?

For author names, we decided to use (our best guess) of the correct casing, even if it was printed in all-caps or all-lowercase in the START metadata or the PDF.

But I don't think we ever made a decision about titles. The situation is different because BibTeX automatically recases titles but not authors. The options I can think of are:

1) Preserve the original casing in the XML (with the PDF taking precedence over the START metadata or the table of contents), and output the original casing in both HTML and BibTeX.

2) Same as (1), but when generating HTML, normalize case (say, according to [APA style](https://apastyle.apa.org/style-grammar-guidelines/capitalization/title-case)).

3) Normalize case in the XML.

Under either (2) or (3), we will need to write a script that does the casing. Shouldn't be too difficult, but we don't have any existing code for it. Because `` annotations are not complete, it will make missing annotations _much_ more visible (IMO a good thing even if temporarily bad).