Python Classwork: Number Stats, Part 1
    Write a Python program named "NumberStatsPart1.py" that asks for,
    and gets from the user, an unlimited number of integers.  The
    user should press the ENTER key after entering each number, and
    should press ENTER on a line by itself to indicate that he/she
    is finished entering numbers.

    After all of the integers have been entered, your program
    should report both the sum and the average (arithmetic mean) of
    all of the numbers entered by the user.  If the average is an
    integer, than display it as an integer, but if the average is
    a decimal number, display it rounded to (at most) two decimal
    places (see the examples below).  If the user does not enter any
    numbers, then do not display the sum or average, but instead
    display an appropriate message (see below).

    Your program does not need to perform any error trapping.  That
    is, you may assume that the user will enter only integers.

    Your program's output should be formatted in a manner similar to
    what is shown below.  You may put all of your code into the main
    area of the program.  Your program should not import or use any
    external functions.


    Example Program Run #1
    ----------------------
    Please enter an integer:

    You did not enter any numbers.  Goodbye!


    Example Program Run #2
    ----------------------
    Please enter an integer:  3
    Please enter an integer:  4
    Please enter an integer:  5
    Please enter an integer:  6
    Please enter an integer:  5
    Please enter an integer:  6
    Please enter an integer:  7
    Please enter an integer:

    The sum of your numbers is:  36
    The average of your numbers is:  5.14


    Example Program Run #3
    ----------------------
    Please enter an integer:  17
    Please enter an integer:  -3
    Please enter an integer:

    The sum of your numbers is:  14
    The average of your numbers is:  7


    Example Program Run #4
    ----------------------
    Please enter an integer:  5
    Please enter an integer:  0
    Please enter an integer:  13
    Please enter an integer:  4
    Please enter an integer:

    The sum of your numbers is:  22
    The average of your numbers is:  5.5