Fix MathJax question rendering

Make MathJax re-typeset the page when questions are loaded, too.

Better MathJax support

Questions to demonstrate MathJax support in Jupyter notebooks. Not yet tested on Jupyter book. Also, because feedback dynamically updates the page, MathJax is now told to typeset math on the page again.

Support for code in answers

This version allows the inclusion of program code in multiple/many choice answers. Code blocks will be formatted appropriately.