Add versioning to API

[madhavajay]

All responses should include a field with API version in the header, starting with 1 for example:

Custom Header:
"X-API-Version": 1

JSON Payload:

{
    "status": "201",
    "message": "Description"
}

[joshlf]

An alternative possibility would be for the client to indicate which API version it expects and for the API to respond with an error if that version is not supported. This would ensure that the API doesn't execute a stateful request only for the client to then learn that it can't understand the response and cannot continue the flow.