MNIST enhanced performance. Faster convergence, better score (#574)
MNIST enhanced performance. Faster convergence, better score (#574)

* MNIST example. Changes batch size from 10 to 16. Improves classification accuracy and convergence speed.

* MNIST example. Limits scaling of learning rate as function of mini-batch traning size.

* MNIST example. Limits scaling of learning rate as function of mini-batch size.

Wangyida/tiny-cnn,Wangyida/tiny-cnn