Takes LongTensor with index values of shape `(*)`

and returns a tensor
of shape `(*, num_classes)`

that have zeros everywhere except where the
index of last dimension matches the corresponding value of the input tensor,
in which case it will be 1.

## Usage

`nnf_one_hot(tensor, num_classes = -1)`

## Arguments

- tensor
(LongTensor) class values of any shape.

- num_classes
(int) Total number of classes. If set to -1, the number
of classes will be inferred as one greater than the largest class value in
the input tensor.

## Details

One-hot on Wikipedia: https://en.wikipedia.org/wiki/One-hot