Symbols in LaTeX text mode (not mth mode)

[Rob Beezer]

(Notes for Oscar and Alex at the end.)

I have been sent on a mini-quest to pay down some technical debt in the LaTeX
conversion (spurred on by trying to facilitate loading alternate math fonts).
The goal: stop using symbols from math fonts as typographic decorations that are
not really mathematics. As a consequence of \blacksquare not being supported in
the first font I experimented with.

So:

* "end of environment" markers have changed slightly. Strictly style, and we
have features that allow for changes.

#proof: unchanged, a solid square (from a new font)

#definition: open lozenge is now a solid diamond

#example: open square is now a solid triangle

If there is a consensus that the solid versions are a bit too "heavy" or too
"black", they could be scaled down slightly.

* Unordered list markers have changed. Shapes are unchanged, but
implementation is different. They are mostly being scaled down some, and lifted
up off the baseline. I think it is a big (subtle) improvement.

* Double arrows, for proof directions (implies/right, implied-by/left). A lot
of experimentation, and nothing I thought was as good. And one might argue that
this is a mathematical operator of sorts (but please don't!). Left unchanged
for now.


@Oscar: I put the new font package and some macro definitions into a template of
its own ("text-symbols") for incorporation into the preamble. Which I do not
think the classic conversion needs for environments. But that conversion will
need it for the unordered list markers, so then I added it in. Untested.


@Oscar: I've tried to concentrate on reliable packages and cross-engine support.
Would you mind building a PDF with both xelatex and pdflatex using the TeX
installs you have in CodeSpaces, etc?


@Alex: the static version of some WeBWorK forms/popup interface elements use
lists with different markers

$\square$: can be implemented identical to \ptxsquare

$\bigcirc$: scale \textopenbullet (as done for #ul now), or try \textbigcircle

$\Box$: a macro definition with "\ding{}" can make nice boxes with shadows

See the recent commits for examples and available overhead, etc.

I think three new "\ptxww...." macros would be a good idea to keep things
separated out


OK, as usual, keep an eye out for oddities. Thanks!

Rob