Changes `createResource` to return an object with `read` and `preload`
methods. Future methods may include `set`, `subscribe`, `invalidate`,
and so on.
* [experimental] simple-cache-provider
Pushing an early version of this for testing and demonstration purposes.
* Change invariant to DEV-only warning
* Use function overloading for createResource type
Expresses that primitive keys do not require a hash function, but
non-primitive keys do.
* More tests
* Use export *
* Make Record type a disjoint union
* Pass miss argument separate from key to avoid a closure