Spec out Application level caching solution

[sjperkins]

It's probably worth thinking carefully about an application level caching solution. @bennahugo @JSKenyon @o-smirnov

Food for thought:

• https://cachetools.readthedocs.io/en/stable/
  • https://stackoverflow.com/a/50963359
• http://www.grantjenks.com/docs/diskcache/