Meta information about a resource.

This is basically the head of the HTTP message: the status code, the reason phrase, and the headers. In the application level callbacks, a reference to an instance of this class can be found in every resource. For example, given the following odd response from the server:

     HTTP1.1 200 OK
     Content-Type: application/json; charset=UTF-8

     {
         "error": {
             "error_code": "BAD_REQUEST",
             "error_message": "The value of foo cannot be bar"
         }
     }
 

     { response ->
       assert response instanceof fi.linuxbox.upcloud.core.Resource
       assert response.META.status == 200
       assert response.META.message == "OK"
       assert response.error instanceof fi.linuxbox.upcloud.resource.Error
       assert response.error.errorCode == "BAD_REQUEST"
       assert response.error.errorMessage == "The value of foo cannot be bar"
     }