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.
I suppose ```err != nil && !os.IsNotExist(err)``` === ```!os.IsNotExist(err)```