updated load and save function. Now also distance maps are stored.

Additional package msgpack-numpy needed for ndarray.
This saves tons of time when loading precomputed files.
Updated test to test loading and saving with and without distance maps
minor update to bug in observation dimension

flatland/envs/observations.py

@@ -22,7 +22,7 @@ class TreeObsForRailEnv(ObservationBuilder):
     For details about the features in the tree observation see the get() function.
     """
 
-
+    observation_dim = 9
 
     def __init__(self, max_depth, predictor=None):
         super().__init__()
@@ -43,9 +43,6 @@ class TreeObsForRailEnv(ObservationBuilder):
         self.tree_explorted_actions_char = ['L', 'F', 'R', 'B']
         self.distance_map = None
 
-        # this needs to be updated when new features are added!
-        self.observation_dim = 9
-
     def reset(self):
         agents = self.env.agents
         nb_agents = len(agents)