[DEPRECATE] Tactile graphics with braille labels

[Rob Beezer]

A long-running experiment converted "latex-image" code (specifically TikZ code)
into SVG and PDF images that could be embossed as tactile graphics for blind
readers. Labels were converted to braille (including math, of course). It was
a good experiment - several of us learned a lot about how hard it is to make
good tactile diagrams.

To support processing labels, we had a "label" element with @offset and
@direction attributes, that could be mixed in with TikZ code.

The experiment is now obsolete, due to the excellent work at David Austin's
PreFigure project (https://prefigure.org). So the pretext/pretext script
routine has been removed along with supporting XSL.

We have deprecated the "label" element, and you will get warnings. The
templates converting "label" to TikZ code remain, so experimental figures you
have going will continue to be produced as versions for sighted readers, exactly
as before. We will leave this code in as long as we can, and will give ample
warning if it needs to be removed.

So consider replacing "label" elements with corresponding TikZ code. If you
produce the LaTeX file for your project, it should have your TikZ code with
substitutions for the "label" elements. You could cut those out and place them
back into your source.

Rob