racket/class: shave a little time from `send`
racket/private/class-internal: protect ids private to class implementation
scriblib/figure: make figure hyperlinks show start of figure

... instead of putting the figure's caption at the top of the
browser window.

I can't decide whether I like the technique here, which is to use
JavaScript to move a figure caption's <a name=...> when the page is
loaded.  On the one hand, fixing up HTML via load-time JavaScript code
seems ugly compared to generating the right HTML in the first place.
On the other hand, it simplifies the generatation of a
backend-independent Scribble document (i.e., don't try to generate
different target locations for HTML and Latex), and HTML-specific
behavior seems properly handled at the HTML/JavaScript level.