Math rendering in documentation: migrate to MathJax or KaTeX?

[stestoll]

Currently, EasySpin uses a home-grown system to generate images from LaTeX equations embedded inside <!--MATH --> comments in the HTML files. These are compiled using the doc builder script.

This has several disadvantages:

• Rendering issues. The currently produced png image files result in displays where the math is not properly lined up with the text. Zooming reveals that the math is pixelated.
• Need for a documentation build step.

There are two excellent web math rendering packages available: MathJax and KaTex. We should evaluate whether to migrate to one of these.