ENH add training score to GridSearchCV.cv_scores_
add docstring for GridSearchCV, RandomizedSearchCV and fit_grid_point. In "fit_grid_point" I used test_score rather than validation_score, as the split is given to the function.
rbf svm grid search example now also shows training scores - which illustrates overfitting for high C, and training/prediction times... which pasically serve to illustrate that this is possible. Maybe random forests would be better to evaluate training times?