Loss functions

[GoodStuff11]

Convert the loss functions into classes, defining their derivatives.

[GoodStuff11]

System has been implemented. More is required:

• cross entropy loss/log loss
• hinge loss
• logistic loss

[GoodStuff11]

This class should have a base abstract class called Optimizer and derived classes for each of the algorithms. It should be fully self-contained, not just having the functions