Implement proper caching library that follows HTTP standards and stores asset age/etags

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control

Packages that take care of most of this:
- https://www.npmjs.com/package/cacheable-request (seems like the best option)
- https://www.npmjs.com/package/http-cache-semantics
- https://www.npmjs.com/package/make-fetch-happen
- https://www.npmjs.com/package/fresh