* Add documentation and API
* Add public keyword
* Implement test_indices (debug version)
* Return indices as Vec of Vec
* Consume vector using drain()
* Use shape() to return num of samples
* Implement test_masks
* Implement KFold.split()
* Make trait public
* Add test for split
* Fix samples in shape()
* Implement shuffle
* Simplify return values
* Use usize for n_splits
Co-authored-by: VolodymyrOrlov <volodymyr.orlov@gmail.com>
