Revert "Fix k-fold CV"

This reverts commit 60de1f13b144cdef027277f873fcd645adf14de0.
Fix Kfold iterator so it returns test set indexes.
Test LOOCV and Kfold are the same for n=k
Update README for Kfold
Merge pull request #5 from lendle/kfoldfix

Fix Kfold iterator