Convert NARK to reStructuredText

[AA-Turner]

This PR converts the Suggested Variable Naming Conventions in the Econ-ARK Toolkit (NARK) to reStructuredText and removes the LaTeX sources. This makes NARK accessible on the website, whereas it was previously only readable as the pre-rendered PDF (or, by rendering the PDF yourself).

The only outstanding problem is the lack of the \mathbbmss macro in MathJax -- see e.g. https://github.com/mathjax/MathJax/issues/792. Would changing it simply to \mathbb be acceptable?

A

cc: @MridulS

(note: this PR is based on top of #1302, only the final 2 commits are part of this PR)