Implement a Redis backend

[arrdem]

Yes I said the R word. I'm a big Redis fan, and while it has plenty of limitations this'd be a pretty good way to implement a "real" server back-end for Shelving if I choose to go full Datomic clone.

It'd be interesting to consider how Shelving could try to offer parameterized / composable shelves which offer consistency and commit operations ala carte, or support a concept of a write cluster independent of a larger read pool.

#scopecreep

[arrdem]

Amusingly this dovetails with #14 in that Carmine already uses Nippy for its serialization layer.