Compute Fibonacci numbers using four different methods:
1) iteratively using R code,
2) via the closed function in R code,
3) iteratively in C using the .C function,
and 4) iteratively in C using the .Call function.
calcFib(n, len=1, method="C")nth fibonacci number to calculate
a vector of length len showing previous fibonacci numbers
select method to use: C, Call, R, closed
Vector of the last len Fibonacci numbers
calculated.