fib function as given in notes.
Tested with fib(8)
rename fib method to fibRecursive
demonstrate problem with negative input
Cleanly handle negative or zero input
report number function calls & number additions
Start to document exercise 2b Fibonacci
code Iterative version
much simplier than recursive and so much more efficient
requires n-2 additions and storage of 3 numbers
Add function with memoization.
Results indicate it is much more efficient than simple recursion but
at the cost of complexity.
Finish Fibonacci write up with conclusions