Changed pruning algorithm.

Currently you are throwing away 20% of your data for no good reason. This PR changes the pruning algorithm from removing the top 10% and bottom 10% to removing values outside of 3 standard deviations from the mean; these values are considered outliers.

I also did some minor formatting cleanup to use `printf` instead of mixing `echo` and `sprintf`.

Note that this also removes the call to `sort`; this is because it is unneeded for the new pruning operation. This may affect the result printer; I am unable to know since I couldn't run tests because my composer install is having issues (globally, not just on your repository).