Update KaTeX Version

[yourealwaysbe]

Is your feature request related to a problem? Please describe.
The current version of KaTeX is 0.13.0, Idyll uses 0.9.0. In particular \newcommand and similar is supported in 0.13.0, but does not appear to be supported in 0.9.0. \newcommand is very useful for serious mathematical articles.

Describe the solution you'd like
Update to 0.13.0.

Describe alternatives you've considered
Could not think of alternatives (except bookdown :) ).

[mathisonian]

This makes sense to me. We'd need to edit the CSS file that gets included (https://github.com/idyll-lang/idyll/blob/master/packages/idyll-cli/src/client/_index.html#L36-L41), upgrade the dependency in idyll-components and make sure the Equation component is functioning properly with the new version.

[mathisonian]

I think we should drop react-latex-patched in favor of https://www.npmjs.com/package/react-latex since that one seems to be more widely used and up-to-date.