Update residual-layers.lua to be consistent with other torch nn models

[lim0606]

Hi,

I updated residual-layers.lua so that it can be used with other available layers in torch community.

I thought this might be useful for someone who might want to use the residual layer in their network architecture.

This might be not the preferred way of @gcr.

Anyway, thank you for sharing your review work.

Best regards,

Jaehyun

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This change is 

[gcr]

I see! Thank you -- I wasn't sure how to express this network in the usual Torch way, so I had to use the nngraph module. This example makes that clearer.

[lim0606]

I just meant that the modification intended to make the layer be look-alike some tutorials in https://github.com/torch/torch7/wiki/Cheatsheet, e.g. https://github.com/soumith/imagenet-multiGPU.torch.

Thank you :)