Multiclass classification support

[GillianGrayson]

Hi!

Does your package support solving the multiclass classification problem?
I found only one mention for multiclass in code:

DeepCTR-Torch/deepctr_torch/layers/core.py

Line 145 in 2cd84f3

if task not in ["binary", "multiclass", "regression"]:

I also found only binary cross entropy loss in models

[joeyzyz]

I guess it may not support multiclass classification currently, see the code below, it is located here:
[loss_func[i](y_pred[:, i], y[:, i], reduction='sum') for i in range(self.num_tasks)])
The prediction is hard-coded into a square matrix, thus y_pred[:, i] is used to predict binary probability.

[joeyzyz]

Also see here, if it is not a binary classification or regression model, it will throw an exception.
https://github.com/shenweichen/DeepCTR-Torch/blob/master/deepctr_torch/models/multitask/mmoe.py#L59