modified the scorers dictionary so that average F1 scores can be computed for binary classification rather than just having f1 for the positive class, which is the default (I believe support for this was added in scikit-learn some time in 2013)
Merge pull request #130 from EducationalTestingService/feature/average_f1_for_binary_tasks

modified the scorers dictionary so that average F1 scores can be computed for binary classification rather than just having f1 for the positive class, which is the default