* add 2/3d adaptive_pooling

* fix format

* fix format

* add en doc rst

* fix format

* fix doc

* fix doc

* refine example code

* unify example code

* add mse_loss_cn doc

* add index

* add index

update demo code in NLLLoss_cn.rst

Update the docs of nn.loss.L1Loss and nn.functional.l1_loss