New variation for Nim#89

I would make a PR since it's a super simple addition but I wanted to see if it would be worthwhile first. Nim supports disabling runtime checks by using -d:danger. This increases its performance substantially. There are already several Nim versions in the "tuned" category so adding another one may not be desirable, but it should place Nim even closer to the most optimized C++ version. From the looks of the implementation, it should be as simple as just tacking on "-d:danger" to the "fast" implementation of Nim.