Classifier/Ranker: Implement distance-weighted reranking using cost-sensitive perceptron, fix bugs in implementation; need to create object to describe an instance, encapsulating a feature vector and app-specific info, and add type param for this to classifier
Classifier: Clean up creation, implement debug-printing of weights
Catch errors during creation of word distributions
Perceptron: Bug fix for NaN's occurring when two instances being compared have identical feature vectors