Merge pull request #21 from h-hirokawa/file-field-response

Add support for FileField response.

tests/reference.yaml

@@ -493,6 +493,13 @@ definitions:
         description: should articles have UUIDs?
         type: string
         format: uuid
+      cover:
+        type: string
+        format: uri
+        readOnly: true
+      cover_name:
+        type: string
+        readOnly: true
   Project:
     required:
       - project_name