Squashed commit of the following:
- Clean up PRO.
- Clean up ScoreStats.
- Clean up ScoreData.
- Clean up ScoreArray.
- Remove unnecessary headers.
- Clean up ScopedVector.
- Clean up Point.
- Clean up PerScorer.
- Clean up Optimizer.
- Clean up MergeScorer.
- Clean up InterpolatedScorer.
- Clean up FileStream.
- Clean up FeatureStats.
- Remove inefficient string concatenation.
- Clean up FeatureData.
- Clean up FeatureArray.
- Clean up Data.
