Support autograd view (a.k.a. reshape) and MNIST using CNN example
- new function/chain for topology operation https://github.com/ShigekiKarita/grain/blob/v0.0.8/source/grain/functions/topology.d
- new example using convolutional neural networks https://github.com/ShigekiKarita/grain/blob/v0.0.8/example/mnist_cnn.d