prompt, default
Prompt the user for a reply string (with optional default).
EXAMPLES
--------

1. Asking for input without providing a default.
   Note that prompt_user keeps re-prompting until the user
   enters something.

    print prompt_user("What is your name")
    What is your name: 
    What is your name: 
    What is your name: Cyclops
    Cyclops

2. Asking for input with a default reply.
   Note that prompt_user substitutes the default string of the user
   presses return without enterring anything.

    print prompt_user("What is your name", "Anonymous")
    What is your name (Anonymous): Cyclops
    Cyclops 
    0>

    print prompt_user("What is your name", "Anonymous")
    What is your name (Anonymous): 
    Anonymous
    0>

3. Allowing the user to enter an empty string.

    print prompt_user("Title", "")
    Title: 

    0>

ARGUMENTS
---------
prompt    -   The string to prompt the user with.

default   -   Optional.
              The string to substitute as the reply if the user
              presses return without entering anything.