add the softsign activation.

fix bug (conv2d  groups: 'num_channels % groups is not 0:' )

enable mkldnn benchmark with googlenet

Fix pool max with index.(Mask type should be int, not float)

Add cudnn pool3d

Add sequence slice operator

remove redundant tests in layer helper's unittest.

Add the configuration helper for multi-head attention.

update the dot_product_attention.

Add the L2 distance layer.

* enforce shape of backward target to be {1}

* fix test_regularizer.py

* rm unused code

* fix backward_test

* fix a type bug

* fix test_program