code: public Counter<L> logProbabilityOf(int[] features) {
      Counter<L> scores = scoresOf(features);
      Counters.logNormalizeInPlace(scores);
      return scores;
    }
docs: Given a datum's features, returns a counter mapping from each
  class name to the log probability of that class.
  Looking at the the sum of e^v for each count v, should be 1.