check_serialization_api_v_1
check_serialization_api_v_2
The difference from version 1:
* when the process is finished the field "_end" appear
* after every pass_milestone() in the object _miliestone_pass gets the
current time (and _miliestone_pass is stored in serialized object)
check_serialization_api_v_3
The difference from version 2:
* Added _is_paused and _elapsed.