Need a multiclass example (1 example multiple classes)

[agibsonccc]

Issue Description

This is a fairly common use case: Sigmoid output Xent output

An iterator that knows how to map a set of files/rows to multiple labels.

Please describe your issue, along with:

• expected behavior
• encountered behavior

Version Information

Please indicate relevant versions, including, if relevant:

• Deeplearning4j version
• platform information (OS, etc)
• CUDA version, if used
• NVIDIA driver version, if in use

Contributing

If you'd like to help us fix the issue by contributing some code, but would like guidance or help in doing so, please mention it!

[turambar]

@agibsonccc are you referring to the setting where each example can have multiple binary labels (as implied by sigmoid output + cross entropy)? If so, I believe this issue should be titled, multilabel rather than multiclass, which refers to the case where you have multiple mutually exclusive labels (or one categorical label).