[pyp-c1-a1] Fibonacci numbers

(http://en.wikipedia.org/wiki/Fibonacci_number)

Write a program that generates the nth number in a fibonacci sequence (starting at 0).

The program should start and ask for two things:

1. The number that will describe the nth term you want to get
2. Whether the function should be recursive or not

The program should count with data validation. This means that the program must inform the user when the number they inserted is invalid.

Extra: If the user passes a --recursive argument, the program should not ask for the function to use and use the recursive function.