Baseline specification from docker/docker#9015

As a baseline for the new registry API specification, we are checking in the
proposal as currently covered in docker/docker#9015. This will allow us to
trace the process of transforming the proposal into a specification. The goal
is to use api descriptors to generate templated documentation into SPEC.md. The
resulting product will be submitted into docker core as part of the client PR.
Justify formatting in specification
Automatically generate V2 API specification

This changeset provides data structures and definitions describing the routes
available in the V2 registry API. These route descriptors are structured to
provide automated registration, for creating routers, in addition to complete
documentation duty. It's also a possibility that this could be used to
enumerate test coverage for server implementation.

Using this functionality, we've also developed a template to automatically
generate and API specification for submission into docker core.
Generate initial V2 API specification
Simplify parameter descriptor declarations
Merge pull request #868 from stevvooe/ng-api-specification

[WIP] Automatically generate V2 API specification