Repeated cross-validation about origami HOT 2 CLOSED

Added two new features that should make this possible for origami in general.

make_repeated_folds will generate fold structures for repeated_cv (e.g. to do 10 repeats of 10 folds cv for 1000 observations you could do make_repeated_folds(10,n=1000,V=10).

cross_validate now takes argument .old_results that will be combined (rather naively) with the results from the current call. This should allow one to add more repeats to a current result set.

I have not added support for repeated cross-validation to origami_SuperLearner because we can instead integrate it into the SuperLearner package when we integrate origami cross-validation there.

from origami.

Awesome, so fast! Much appreciated

from origami.