UNIX dependent features and general utilities.

1. Command-line arguments, timing and system calls :

     ucmdline         Unix_Command_Line
     rusage           Unix_Resource_Usage
     timing           Timing_Package
     system_call      System_Call
     machines         Machines
     byemess          Bye_Bye_Message

2. Dialogues with user
 
     commuser         Communications_with_User
     file_ops         File_Operations
