Integrating Jordan's proof of concept

[captbaritone]

I've been working on a similar userland API for concurrent store and @thejustinwalsh and I just had a chance to catch up about joining forces. My exploration can be found here:

• Proof of concept code
• Tests for POC code

Just to recap next steps from our meeting this morning:

1. Port test cases from my test suite to this repo (some may fail, especially the selector ones)
2. Assuming we feel convinced the provider component is needed, adopt the strategy used in my prototype in this repo
3. Adapt the prototype to support passing the store as an argument to the hook. We can start with restrictions like: "It's an error to change the store of an already mounted hook" and "It's an error to create stores while the provider is mounted"
4. Investigate unneeded renders when state does not change. Can we find a way to avoid calling setState when the value should not result in a new render?

[captbaritone]

I believe this should solve #2