As we expand beyond Parsoid we need a generic way to cache relatively simple responses from backend services. We should make this module fairly generic, so that we can easily configure it to support many services with similar caching needs.
- Provide an internal service end point, and map requests to storage or backend service requests. The backend request format needs to be configurable.
- URI format in spec needs to define `key` and optionally `revision`.
- Store responses from GETs, and only if no query parameters were supplied.
- Optionally (if configured) support refreshing content with a `Cache-control: no-cache` header.