Msg class
  - methods to set a field, get a field, get full transmission string
  - fixed format and enums,
          store in fixed struct and convert one by one vs
          store in struct of char*'s that can cast to single char*
  - xml and load format, store in array of char*'s,
            cast to char* to send
    possibly format msg itself in xml
  - variable field inclusion 
          field type, field size, field content vs 
          is-it-there flag + fixed format if it is
  - kinds of fields
        - msg type, ack/noack, msg id, sender id, password, 
          reply to addr, reply to port, message target, local time sent, 
        - app specific fields
          location, task, activity, message text
  - additional (non transmission) fields for 
               time received, addr received at, port received at