[NEW] Linking from a PDF to Asymptote graphic

[Rob Beezer]

A 3D Asymptote diagram is an HTML file that is interactive (rotate, scale,
etc.). You can now configure the electronic PDF to link to this file.

Example: Figure 9.11 in
https://pretextbook.org/examples/sample-article/derivatives.pdf

Documentation: https://pretextbook.org/doc/guide/html/latex-asymptote-links.html

Thanks to Sean F for getting this started. Another killer feature for killer
APEX Calculus.

Rob