Adds prototype NG driver apis

Includes an IPC system for out-of-process drivers so users won't have to recompile the registry to bring their own drivers. Also, drivers can potentially be written in any language with a functioning [libchan](https://github.com/docker/libchan) implementation.
In terms of previous filesystem driver configuration, there was a lot more than just the root directory. For example, in the S3 driver, you had to set up your access key/secret key to connect to the S3 bucket. For the swift driver, you needed to specify your tenant name, region name, your keystone API key, etc. How will this fit in with this implementation?