Add code to deal with MSG_DONE.
If a process finishes, the master process will add it to done_list, and done_count will increment.
Add code to deal with TAG_DATA.
When a slave tells the master that it is sending data, the master will then attempt to receive a message of the size of the previous message's contents.
Add assert statement to avoid buffer overflow.
Assert statement added prior to receiving data from slave process in order to ensure that the size of the incoming data is smaller than the maximum size (max_data). max_data should be equal to the greatest possible level.