added data attribute back with deprecation warning

nd2reader/model/image.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 
 import numpy as np
+import warnings
 
 
 class Image(np.ndarray):
@@ -97,3 +98,8 @@ class Image(np.ndarray):
 
         """
         return self._z_level
+
+    @property
+    def data(self):
+        warnings.warn("Image objects now directly subclass Numpy arrays, so using the data attribute will be removed in the near future.", DeprecationWarning)
+        return self