Add ability to create a local cache instance

[lindskogen]

We're generating a lot of cache keys in our app, and would like to clear all keys under a specific "namespace".

1. My first idea was to add the ability to clear keys by prefix, but searching through all the keys seems like a bad idea for perf.
2. My other suggestion is to create a cache specific to each use-case in the app, and a clear function to delete the whole list in that namespace.

This seemed like more in-line with the direction the React team are taking with scoped cache.

We're already using this solution in our production app with great results :)

[joshuaellis]

Thanks for the PR, i'm gonna be honest here, you really haven't put any information as to the problem you're trying to solve, why this solves the issue, why you think we should resolve the issue. So if you can edit your description to be a thorough PR description this can be considered.

If you need some help take a look at this: https://github.blog/2015-01-21-how-to-write-the-perfect-pull-request/#approach-to-writing-a-pull-request

[lindskogen]

Sorry. I updated the description now!