Two space leaks, squashed by using a strict accumulator.
Fix space leak in indexInto
Classic foldl with a lazy accumulator. Alternatively, the entire `indexInto` function could be replaced with `Data.List.elemIndex`.
Fix spaceLeak in countConflicts
Using a `foldr` to do a summation, resulting in a space leak. Fixed by switching to `foldl'` and then forcing the elements inside the pair.
Add a missing import following #64