Update PoC and features with the 204 -> 404 update

Closes #33

spec/test/features/data/handler/error_itemnotfound.feature

@@ -12,5 +12,5 @@ Feature: Fail to retrieve nonexistent resource items in Kapow! server.
       | GET    | /foo        |
     When I send a request to the testing route "/foo"
       And I get the resource "/request/params/meloinvento"
-    Then I get 204 as response code
+    Then I get 404 as response code
       And I get "Resource Item Not Found" as response reason phrase