* add batch_norm_layer

* add img_conv_group layer and test

* add check to Tensor.type()

* forward can run

* with backward

* change label data time from int32 to int64

* refine code

* follow comment

* Init file

* Update

* Update

* Complete conv net of MNIST

* Init

* unify layer names

* Update

* Add pool2d layer

* Test recognize_digits_conv

* Clean up