Add functionality to ignore certain labels from being flattend

cdplib/FlattenData.py

@@ -175,7 +175,7 @@ class FlattenData():
 
         return dictionary
 
-    def flatten_if_not_flat(self, data: pd.DataFrame):
+    def flatten_if_not_flat(self, data: pd.DataFrame, labels_to_ignore: list = None):
 
         for data_type in data.dtypes:
                 if data_type == object: