added script for computing evaluation statistics from existing inputs and predictions
added unit test for compute_eval_from_predictions.py, modified setup.py
fixed next() call for 3.3 compatibility
fun with rounding.  python 2 rounds toward infinity whereas python 3 and numpy use bankers' rounding.
fixed some style issues that the linter did not catch
Merge pull request #113 from EducationalTestingService/feature/compute_eval_script

Added script for computing evaluation statistics from existing inputs and predictions.