Swagger docs

Issue: #5893 (points 9 and 10) 

This is a proof of concept for documenting the API with a [swagger](http://swagger.io/) spec. It is far from complete. I wanted to open this PR to gauge interest in this approach. If it's well received I'll look into integration with the existing markdown docs and figure out how to disable the interactive feature.

The interactive querying with the nginx proxy might work as a docker image for "learning the API", as a way for users, or client library developers to test and interact with it. But it isn't going to work for the official docs on https://docs.docker.com/reference/

To view the docs follow the steps in the `README.md`.

The docker container includes the swagger-ui static resources and an nginx config to support the interactive querying.