Produce and harvest QR codes for lesser reading systems

[rbeezer]

A QR code for a YouTube video, or one of our "standalone" pages for interactive is used throughout our LaTeX conversion, since PDF is not very interactive.

They would be useful elsewhere, such as in EPUB. So having a routine in PreTeXt core to get the links, build PNG images, and stash them in a "generated" directory would be a great help.

Use some (commonly) available Python library, ideally pip-installable for the CLI, such as described here:

https://towardsdatascience.com/generate-qrcode-with-python-in-5-lines-42eda283f325

[rbeezer]

On pretext-dev @rbeezer just wrote:

Perhaps we could even rip this out of the LaTeX code. It works like a charm, but is time-consuming on the first pass of a fresh build.

[StevenClontz]

Strong vote to do QR code generation in Python, not in LaTeX. Every build uses Python, not every build uses LaTeX.

[rbeezer]

This got underway at ebd94b8ed16f32563c085f189c495bc6bc54324d and will migrate into the static versions of interactive.