* Add new API: paddle.prod

test=develop

* fix the doc of dot

(1) Add api paddle.reshape(x, shape, name); 

(2) Use Tensor replaces Variable. test=develop

* rename input

* add unittest, test=develop

* use paddle.data instead of fluid.data, test=develop

* 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

* 1.Fix api sum:(1) input->sum; (2)dim->axis; (3)keep_dim->keepdim.

* 2. fix bug when len(axis) == len(x.shape). 

align expand_as op to expand.

* Update `paddle.add`

remove `alpha`
update doc sample code
remove `:alias` etc

* Remove `imperative` reference from docstring

* adaptive expand op to 2.0 (align to torch.expand) , test=develop

* 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 tile_op, test=develop

* fix the doc of inverse, dot, cholesky

Update the code for the min,max, test=develop

* Add the max, min, maximum, minimum api for the API 2.0, test=develop

* fixed imperative module in doc example code

* fixed static module

* solve conflict

add deprecated decorator, remove alias for cumsum op

* Directory migration, test=develop

* Change imperative from paddle init to paddle framework, test=develop

* Fixed jit bug, test=develop

* default static mode, test=develop

* fixed format and create parameter belongs to framework, test=develop

* Fixed import package, test=develop

* fix __init__ format, test=develop

* fixed alias problem

* fixed paddle.enable_imperative problems, test=develop

* Add unittest

* delete install_check comment

* Fixed unittest timeout

* fixed unittest error

* move Program default_xx_program to static package

* optimize unittest method

* fixed framework __init__ format

* fixed jit path

* delete alias

* move jit to paddle

* Fixed unittest format

* fixed paddle.default_main_program

* Fixed save load API in paddle __init__.py

* fixed ci paddle.imperative.to_variable

update cumsum api and fix up the cumsum op

1. update document template for unary elementwise layers(a.k.a. activation layer);
2. remove generate_op_noattr and use generate_activation instead; remove redundant function copies;
3. minor update for docstring to fix rst format errors.
4. fix doc for Rsqrt OP
5. add sample code for each activation separately;
6. remove the unused deprecated decorator.

* Change use_quantizer attribute name and data type

* Fix problem with setting attribute

* Add changes due to review

* Small change in function

* Restore use_quantizer attr for compatibility

* refine unsqueeze, test=develop

* update unsqueeze, test=develop

* refine unsqueeze, test=develop

* refine unsqueeze, test=develop

* update

* remove None, test=develop

* follow comments

* support bool

* update doc

* follow comments

* merge develop

* refine stack in dygraph mode, test=develop

* update stack, test=develop

* rename Variable to Tensor, test=develop

* add name args to fluid.layers.stack, test=develop

* follow comments

* update doc

* update doc

* follow comments

update the sort api, delete unused ouput index tensor

* test=develop,test=document_fix, remove the out args

* Revert "test=develop,test=document_fix, remove the out args"

This reverts commit f430799b.

* test=develop,test=document_fix, remove the out args

* remove all  the out args

* remove all  the out args

* test=develop, remove all  the out args

* test=develop, remove all  the out args

* test=develop, remove out args in matmul testcase

* test=develop, fix the bugs of out args testcase in logsumexp

* test=develop, fix the bugs of out args testcase in elementwise_add

* test=develop, fix the bugs of out args testcase in elementwise_div

* test=develop, fix the bugs of out args testcase in activation

* test=develop, fix the bugs of out args testcase in addcmul

* test=develop, fix the bugs of out args

* test=develop, fix the bugs of out args in API example

* test=develop, fix the bugs of out args in kron testcase

* test=develop, fix the bugs of out args in kron testcase

* test=develop, remove out args

* test=develop, remove out args

* test=develop, fix the coverage

* test=develop, polish codestyle

* test=develop, Update math.py

* test=develop, polish codestyle

* test=develop, polish codestyle

* test=develop, polish codestyle

* test=develop, polish codestyle

* test=develop, polish the test_activation_op.py

* test=develop, Update math.py

* test=develop, fix the failed CI

* test=develop, add core.ops

* test=develop, add core.ops change clamp to clip

* test=develop, add core.ops change clamp to clip

* test=develop, write testcase for clamp OP

Update the code for the compare_ops, update the api and doc 

Fix the argsort and sort op for the api2.0, and update the api 

fix the cross OP behavior is not as expected when axis=0