API versioning

[silverAndroid]

As mentioned in issue #21, we should use API versioning for backwards-compatibility since we can't assume all users will update their application so I think we should introduce API versioning in case we want to make drastic changes to the API responses

[lirantal]

Take a look at https://github.com/lirantal/express-version-route
We've been using it across some projects at work, and I'd be happy to help with a PR to integrate it though it's a pretty simple and flexible express middleware.