Rename answer->candidate
Don't memoize document titles, user names, etc. to avoid increasing size of weight vector
Rerank: Major rewriting to clean up classify/rank/perceptron code, generalize feature and weight vectors, redo reranking algorithm to (hopefully) be correct using multi-label classifier
Perceptron: Add debug version of multi-label perceptron, to debug algorithm
Memoizer: Break number_of_entries into number_of_stored_entries / number_of_valid_indices
FeatureVector: Some cleanups for sparse feature vecs, including an object for creating compressed ones directly (without using a SparseFeatureVectorFactory/memoizer)