docs: def usage (exit=False):
    """usage([exit])
  
    Prints the usage statement at the top of a Python program.  A usage
    statement is any comment at the start of a line that begins with a
    double hash marks (##).  The double hash marks are removed before
    the usage statement is printed.  If exit is True, the program is
    terminated with a return code of 2 (GNU standard status code for
    incorrect usage).
    """
    stream = open(sys.argv[0])
    for line in stream.readlines():
      if line.startswith("##"): print line.replace("##", ""),
    stream.close()
  
    if exit:
      sys.exit(2)