feat: add accessor and iterator method on data field

jwebsite/content.py

@@ -56,6 +56,13 @@ class DataField:
     def __str__(self) -> str:
         return str(self.__value)
 
+    def __getitem__(self, key: Any) -> Any:
+        return DataField(self.__file, self.__value.get(key))
+
+    def __iter__(self) -> Iterator[Any]:
+        for it in self.__value:
+            yield DataField(self.__file, it)
+
 
 class DataFile(Content):
     def __init__(self, path: Path) -> None: