text: Title: Additional Evaluation Metric / Imbalanced Problems
  Body: There are several evaluation metrics that would be particularly beneficial for (binary) imbalanced classification problems and would be greatly appreciated additions. In terms of prioritizing implementation (and likely ease of implementation I will rank-order these):
  
  1. **AUCPR** - helpful in the event that class labels are needed and the positive class is of greater importance. 
  2.  **F2 Score** - helpful in the event that class labels are needed but false negatives are more costly.
  3.  **F0.5 Score** - helpful in the event class labels are needed but false positives are more costly.