text: Title: Customization of Precision Recall curves 
  Body: It would be best to add ability for the user to select which curves they want to display. E.g some people might not want to display the macro and micro averaged curves, display only a specific class' ROC curve.
  
  This approach could then be extended to Precision Recall curves as well 
  
  EDIT: ROC Curves now has `curves` argument thanks to @doug-friedman 