Major updates
- New plot_cutoff()
- Shows healthy and sick distributions and shows FP, FN, TP and TN depending on a cutoff point
- New remove_layers_cutoff_plot() functions
- Get's rid of layers of a cutoff_plot: FP, FN, TP or TN
Minor updates
- Fix for CRAN change in docType
- Use linewidth instead of size
- Faster implementation of a step in min_possible_prevalence