* add alpha_dropout in nn.functional and nn.layer, test=develop

* refine Interface and assertion, test=develop

* fix ci import error, test=develop

* fix alias and use layers.scale, test=develop

* fix doc and training params, test=develop

* refine details in doc, test=develop

* fix doc details, test=develop

* update Conv2d Conv3d conv2d conv3d api

* update conv_transpose api

* add binary cross entropy with logit loss

* [API2.0] add dropout, dropout2d and dropout3d, test=develop

* refine Interface and assertion after review, test=develop

* fix alias p=1 and use scale, test=develop

* fix doc and training, test=develop

* fix doc in Dropout2D, test=develop

* add functional ctc_loss and CTCLoss class.

* modified docstring of ctc_loss and CTCLoss

* add cross_entropy to nn/layer and nn/functional, test=develop

* use functional/cross_entropy in layer/CrossEntropy

* use functional/cross_entropy in layer/CrossEntropy, test=develop

* add adaptive_avg_pool2d

* add adaptive_avg_pool3d

Fix the API of bce loss and add functional API binary_cross_entropy 

* add pad func

* add pad

* test=develop, add pad op and apis

* restore pad2d

* test=develop, fix paddl declare

* fix pad interface

* test=develop, fix pad

* test=develop, add all pad api and cos_sim

* test=develop, remove padding default value

* test=develop, rename var to tensor

* test=develop, add more tests

* test=develop, rename tovar to totensor

* test=develop, fix init

* test=develop, add more test

* test=develop, add more tests

* add SyncBatchNorm,test=develop

* logsigmoid and LogSigmoid, test=develop

* add elu gelu relu, test=develop

* update to_variable to to_tensor, test=develop

* address review comments, test=develop

* address review comments, test=develop

* change to_variable to to_tensor in test, test=develop

add nn.functional.normalize API for API2.0, fix L1Loss API typo, test=develop

* upate the target to label, test=develop

* Update the code for the margin_ranking_loss, test=develop

Update the sigmoid, Sigmoid layer for the api2.0

* expose and unify the Tensor concepts to the user

* expose tensor to user

* add copy place for Tensor

* add copy place for Tensor

* add note

* add macro PADDLE_WITH_CUDA

* remove RUN_TYPE=DIST

* fix some error

* add Class KLDivLoss and function kl_div

add the api and doc for the margin_ranking_loss and MarginRankingLoss

change api name eps to epsilon for the pair_distance 

* add nll loss API, update demo code of the comment

add pairewise distance for the paddlepaddle api 2.0

fix paddle.nn.loss.L1Loss OP, add paddle.nn.functional.l1_loss OP for API2.0

* add Pad2D and Leaky_ReLU, test=develop

* update,test=develop

* change name,test=develop

* add unittest and redine docs,test=develop

* test=develop update interpolate & upsample api

* add alias in paddle.nn and paddle.tensor test=develop

* add alias in paddle.nn and paddle.tensor dir test=develop

* fix same conflict manually test=develop

* update fc and dygraph alias test=develop

* fix initalizer.py typo test=develop