Update PoC and features with the 204 -> 404 update

Closes #33

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

@@ -4,21 +4,21 @@ Feature: Fail to retrieve resources from nonexistent handler in Kapow! server.
 
   Scenario: Try to get a valid resource path from a nonexistent handler.
     A request to retrieve a resource from a
-    nonexistent handler will trigger a not found
-    error.
+    nonexistent handler will trigger
+    a handler ID not found error.
 
     Given I have a running Kapow! server
     When I get the resource "/request/path" for the handler with id "XXXXXXXXXX"
     Then I get 404 as response code
-      And I get "Not Found" as response reason phrase
+      And I get "Handler ID Not Found" as response reason phrase
 
   Scenario: Try to get an invalid resource from a nonexistent handler.
     A request to retrieve an invalid resource
     from a nonexistent handler will trigger a
-    not found error even if the resource is
-    invalid.
+    handler ID not found error
+    even if the resource is invalid.
 
     Given I have a running Kapow! server
     When I get the resource "/invalid/path" for the handler with id "XXXXXXXXXX"
     Then I get 404 as response code
-      And I get "Not Found" as response reason phrase
+      And I get "Handler ID Not Found" as response reason phrase

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