implement as higher order module

[rt2zz]

• proxies through all 7 redux-persist exports
• merges in immutable config for createPersistor, persistStore, and autoRehydrate

notes:

• I added one overly basic test, so this could definitely use more testing both of the automated and manual variety.
• I recommend we rename this project to redux-persist-immutable
• It feels like REHYDRATE should fire with an immutable map, but to achieve this we would need to add yet another state operator to createPersistor config. Not sure...

[rufman]

One though I had (which I haven't really thought out to completion) is implementing this more like a redux store enhancer. That way the redux-persist version used isn't tied to the version used by this package.