Change footnotes to details/summary

[ascholerChemeketa]

Implementation for footnotes as detail summary.

Goes with:
PreTeXtBook/CSS_core#81

See there for pics

[rbeezer]

Lots of complicated stuff goes into making footnotes, so I restored some "WTH" functionality.

This makes one consequential change (which sort of contradicts our discussion a few days ago).

span.ptx-footnote__contents is div.ptx-footnote__contents

This is more backward-compatible with what we have notw (such as when there is a cross-reference to a knowl, which is supported, even if a bit odd).

Maybe that means adjustments to the CSS on PreTeXtBook/CSS_core#81 has to change with an upate via a new commit.

It is easy enough to make the div a span but will be more of a change in places not directly involved in this PR (side-effects).

Beta with these changes, and items to test with PreTeXtBook/CSS_core#80:

https://pretextbook.org/beta/footnotes-20231024

I might fine-tune teh HTML PR a bit more, but this should be good for David to test, modulo div/span.

@davidfarmer - you tell me what you want for a new vwersion number (0.83?) and I'll make that change as I button this up.

[rbeezer]

Two small comments:

• My take on relevant CSS is that span -> div does not matter, other than maybe removing a display: block.
• I have a branch ready to layer on this which will obliterate the (temporary) manufacture of cross-reference knowls for (original) footnote content.

[rbeezer]

All done. I edited this pretty heavily to bring back content creation for cross-reference knowls, but silently melded into the one commit here. Sorry this one has been sort of slow-motion. But very glad to get these fake knowls out. Aah, I have another commit to get rid of that dead code!