v0.6.0

• Add CorrelationRemover preprocessing technique. This removes correlations
  between sensitive and non-sensitive features while retaining as much information
  as possible
• Add control_features to the classification moments. These allow for data
  stratification, with fairness constraints enforced within each stratum, but
  not between strata
• Update make_derived_metric() to use MetricFrame
• Assorted small documentation fixes