Allow users to serialize custom classes. (#393)

* Allow serialization of custom classes.

* Add documentation and test cases, also fix pickle case.

* Don't allow old-style classes.

lib/python/ray/array/distributed/core.py

@@ -16,14 +16,6 @@ class DistArray(object):
     if self.num_blocks != list(self.objectids.shape):
       raise Exception("The fields `num_blocks` and `objectids` are inconsistent, `num_blocks` is {} and `objectids` has shape {}".format(self.num_blocks, list(self.objectids.shape)))
 
-  @staticmethod
-  def deserialize(primitives):
-    (shape, objectids) = primitives
-    return DistArray(shape, objectids)
-
-  def serialize(self):
-    return (self.shape, self.objectids)
-
   @staticmethod
   def compute_block_lower(index, shape):
     if len(index) != len(shape):