Added StringDelimiter; revised PersonModel

Jeff - thanks for the insight that 0 in JS evaluates to false. I fixed the logic so an age of 0 (because 9-month-olds are alive and screaming, too!) evaluates to true.

Also I added my first take on String Delimiter; any comments welcome. Credits also go to Nicholas Weber, who I had a coding party with for this assignment.
This solution works but see if you can get it to work without using slice or indexOf.