Add circular momentum

[dgarlor]

Based on the new paper of Smith ( https://arxiv.org/abs/1803.09820), I included the momentum variation in your code.

I hope it helps and thank you a lot for your implementation

[uzi0espil]

This is a nice addition to the callback. I have just one question, what if the optimizer used has no momentum property and the user enabled it?

I think self.use_momentum should be a class property where it should take into consideration use_momentum parameter passed by user and check if the self.optimizer has momentum within.