Serialize parsed build-in KaTeX macros

I.e. save the output of katex.renderToString to JSON or some other format. This approach would ensure minimal load times no matter what KaTeX is doing, and possibly provide some good portability.

Off the bat JSON.stringify doesn't work due to circular references though that can be overcome: stackoverflow.com/questions/10392293/stringify-convert-to-json-a-javascript-object-with-circular-reference