Prelegal Wonder

It would be nice to have more cloud storage options than just S3 and I was wondering if it'd be hard to adapt the [Azure](http://godoc.org/github.com/Azure/azure-sdk-for-go/storage) support [currently used](https://github.com/docker/distribution/tree/master/registry/storage/driver/azure) in Docker...

It would be nice to: - have the ability to delete multiple backups / snapshots at once - qualify those multiple backups / snapshots by criteria like age, or tag...