Duplicate links don't work on the print page

[Michael-F-Bryan]

On rust-lang/rust-by-example#989 they found that when two pages in different chapters use the same footnote (e.g. [1]) then one will clobber the other when all chapters are concatenated to form the print page. Ideally we should be able to tweak the print page so this doesn't happen.

@projektir's original comment:

So... this one is funky. There are two pages in RBE that are attempting to use the [^1] annotation. The way pulldown-cmark does annotations is by creating a div with id equal to the annotation name (in this case, "1"). This is all well and good, until the print.html page is created, in which case this now results in two different divs with id="1", which is invalid and is a failure to the linkchecker.

I've replaced 1 here with the dagger symbol †, which looks like 1 in the fonts used by RBE, but I am not really sure how to address this issue in general since we basically can't use the 1, 2, 3 footnote style for as long as we intend to have a page that concatenates everything together.