Updating "mathjax in use"

The MathJax in Use page on mathjax.org leads to several pages on mathjax.org. It has recently been edited to give a concise introduction to the various ways people are using MathJax.

There was page on this wiki at MathJax in Use which corresponded to all of them -- it's been transferred back to mathjax.org and can be found here.

When updating one of the pages on MathJax.org make sure to update the extended-list page as well.

tl;dr the extended page can be a bit wilder -- collect everything that looks interesting -- but keep the other pages small so that people aren't overwhelmed.