ENH: html: append the top title to the document title

[westurner]

It would be helpful for SEO and for usability to include the "top title" in the page titles:

• "top title": "Think Stats"
• document title: "Distributions"
• current <title>: "Distributions"
• suggested <title>: "Distributions [sep] Think Stats"
• sep: —, –, ·

Unfortunately, I don't know how to do this w/ LaTeX.
e.g. Think Stats defines \thetitle, \thesubtitle, and \theversion commands that return strings, but IDK what a good convention would be. https://github.com/AllenDowney/ThinkStats2/blob/c76e1ecdd56a47bbb7ed13ed2fafe1eb1274f3d9/book/book.tex#L45-L47

Maybe a redefineable command?

hevea/html/hevea.hva

Lines 300 to 305 in ee94951

	\@print{<title>}%
	\ifu\@title\jobname\else
	\@notags{\begin{@norefs}\let\@print@u\@print@u@default\@getprint{\@title}\end{@norefs}}
	\fi
	\@print{</title>
	}%