NG: Configuration parser

Implements the configuration spec as defined in #646 with initial configuration version 0.1.
@dmp42 @wking @visualphoenix 
On Mon, Nov 03, 2014 at 03:31:25PM -0800, Stephen Day wrote:
> Should there be a `ParseVersion` function? Will the YAML library
> automatically extract this type?

Or have the version be an [major, minor] list [1].

[1]: https://github.com/docker/docker-registry/issues/646#issuecomment-60689343