Switch docs to use LaTeX instead of images

[henrygerardmoore]

Currently the docs don't render well if you're in dark mode on github. Github supports inline LaTeX with MathJax, so this PR switches the docs to use that. It also removes a dead link. Here's a screenshot showing the difference (previewing in VSCode) where the bottom equation is using MathJax and the top one is the current image. This change also makes modifying the equations or creating new ones easier.

In reviewing, please do make sure I didn't make any typos in the LaTeX translations, and also feel free to add or change line breaks to make the .md files more readable 😄

[henrygerardmoore]

This link is dead, but if there is another image that works well as an example here, feel free to add or request me to add it.

[henrygerardmoore]

This all looks nice in vscode, but it seems that github has some MathJax rendering bugs that mean it doesn't look as nice online. I'm not going to close this PR preemptively but I understand if you prefer the original images.

Looks like this is somehow just an issue with my browser 😁