kfre 0.1.8a3

• new functions for classifying outcomes and ckd stages
  • calc_esrd_outcome,
    class_ckd_stages,
• new functions for performance assessment:
  • plot_kfre_metrics,
  • eval_kfre_metrics,
    • roc_auc curves
    • precision-recall curves
  • performance metrics:
    - Precision/PPV
    - Average PRecision
    - Sensitivity
    - Specificity
    - AUC ROC
    - Brier Score
• new function to generate random ckd data:
  • CKDDataGenerator()