Define the congress api in terms of the OpenAPI specification

[geofflittle]

Define the congress api in terms of the OpenAPI specification [1]. This allows automated server, client, and documentation generation.

Please see tools that implement the spec like swagger [2] which, given a compliant API spec, can generate both server and client code via Swagger CodeGen.

[1] - https://github.com/OAI/OpenAPI-Specification
[2] - https://swagger.io/