Adds the np encoder for JSON arrays

plio/io/io_json.py

 import json
+import numpy as np
 
 
+class NumpyEncoder(json.JSONEncoder):
+    def default(self, obj):
+        if isinstance(obj, np.ndarray):
+            return obj.tolist()
+        elif isinstance(obj, datetime.date):
+            return obj.isoformat()
+        return json.JSONEncoder.default(self, obj)
+
 def read_json(inputfile):
     """
     Read the input json file into a python dictionary.