Weighted Cross Entropy loss function

[Jorisfournel]

Hi,
First thank you for this implementation.
I didn't test it yet but I'm about to, for custom data, a 3 classes segmentation task,
where implementing a weighted cross entropy function should be determinant.
What changes in the code should be done to do that ?
(I don't master tf yet, I worked on caffe before, a tip would be gratefuly taken)

Thanks in advance !

[eragonruan]

@Jorisfournel in nets/model.py, you should modify this function. tf provide weighted cross entropy api, you can find it here