Add a benchmark computing a Fibonacci number recursively
Add a benchmark computing a Fibonacci number recursively

test fibonacci_iterative ... bench:           5 ns/iter (+/- 0)
test fibonacci_join_1_2  ... bench:  23,095,202 ns/iter (+/- 3,561,531)
test fibonacci_join_2_1  ... bench:  21,790,016 ns/iter (+/- 6,379,732)
test fibonacci_recursive ... bench:  12,505,376 ns/iter (+/- 723,289)

The iterative one is just to show how awful recursion is for this. :)

cuviper/rayon,cuviper/rayon