Support for Hypermedia Links

[Mcklmo]

It would be useful to be able to link operations to another. Hypermedia links can link endpoints that are commonly used as follow-up to the current endpoint. The links could be defined on operation creation and be added to the API response automatically.

Example response to GET /users/1

{
  "id": 1,
  "name": "John Doe",
  "email": "[email protected]",
  "_links": {
    "self": {
      "href": "https://api.example.com/users/1"
    },
    "update": {
      "href": "https://api.example.com/users/1",
      "method": "PUT"
    },
    "delete": {
      "href": "https://api.example.com/users/1",
      "method": "DELETE"
    }
  }
}

This could, for example, be achieved by adding a parameter to the Operation struct that is called "HypermediaLinks" that takes a string slice of operation ids. On the api creation, it should panic if a linked operation is not found.