Adding back removed template.
Using  everywhere instead of .katex files.
Adding md5 check to avoid re-rendering templates.
Updating rendering to use HTML entities instead of writing UTF-8.
Adding template render step to Makefile.
Mostly updated bayes-law-primer.
Adding script to replace MathJAX with KaTeX blocks.

Used script on conditional-probabilities-in-thinking.
Also fixed broken anchor in bayes-law-primer (caused by
Jinja2 interpreting as a comment).