Support for Loss Functions (Non-Symmetric Loss function)

[s0nicboOm]

Summary

Support for Non-Symmetric Loss Functions.

We are ultimately looking to support loss functions that are not only in PyTorch but also provide a flexibility to the user to plug in there own custom loss function. This issue does not only point to adding more loss functions but also asks for a better way of providing that interface to the user to bring in their own custom loss function that integrates with the models that we have today.