Define API versioning

We need to define and implement how we are going to deal with API versioning.

I think the best way to do this going forward would be to use a custom header as defined in the REST API guidelines site https://restfulapi.net/versioning/. This allows constant URIs, and removes the burden of hacking together an Accept string.

Proposed solution:

New headers Accept-Version: Target API version Deprecation: Header to warn the user that the endpoint has been deprecated since version N. This allows a more natural period of degredation. While not yet official, this header is WIP from ietf https://tools.ietf.org/html/draft-dalal-deprecation-header-00

Using custom code, we can keep old functionality in some working state going forward, detecting on Accept-Version and passing a Deprecation header to inform the user/endpoint.

This has been merged in and completed.

Created by: sdatspun2

@autumnfound, @chrisguindon Thanks for incorporating the Deprecation HTTP header. The name of the header is Deprecation as you can see from https://datatracker.ietf.org/doc/draft-dalal-deprecation-header/ .

Example

Deprecation: Sun, 11 Nov 2018 23:59:59 GMT

Thanks. @sdatspun2 @dret