Replace recursion with loop

With recursion, benched at about 69000ns.
With loop, benched at about 42000ns.
Remove recursion from fitting; fix incorrect implementation

In my initial translation I changed everything to uint accidentally,
which made a check that a number was positive nonsensical, so it was
removed. I should have had the parameter to fitting be an int, though,
since otherwise fitting would always just return true.
Merge pull request #14 from jonsterling/remove-recursion

Replace recursion with loop