Forgot that only want to add the delta if subelements changed.
Refactored serializable method: all the code that is now in
create_internal_map_delta can be shared between all the
serializable_var_tuple_for_network methods.  Next commit will be to
fill in stub code for other serializable_var_tuple_for_network methods.
Finished rest of map serialization code for single threaded variables.
Started adding traditional container methods to single threaded
container object (eg., get_val_on_key, set_val_on_key).  Note that I
had to split Waldo's get_val_on_key into two separate functions
because the Python code had different return types depending on
whether was returning a map/list/etc.