* update gradient comment in Variable API, test=develop

* add sample code for Variable's gradient api, test=develop

test=develop

test=develop

* add astype api in Variable and refine code style

* add astype api in Variable and refine code style

* add astype api in Variable and refine code style

* refine doc

* fix DataFeedDesc set_batch_size, set_dense_slots cn api doc test=document_preview

* fix continuous_value_model op cn doc

* fix some rst error

* add cpu support only in cvm op

* add explain of N in cvm

* doc fix

* build strategy api doc

* fix train_from_dataset and infer_from_dataset
* fix DataFeedDesc, set_use_slot and desc

* fix Varaible doc

* fix LOD to LoD

* fix LOD to LoD

* test=develop, refine doc

* test=develop, refine doc

* test=develop, refine doc and example code of Variable_cn.rst

* refine fluid.layers.one_hot

* update one_hot doc

* fix code error

* refine docs of CUDA and CPU places, test=develop

* refine docs of CUDA and CPU places, test=develop

* refine cuda_pinned_places, test=develop

* refine, test=develop

* refine, test=develop

* refine scope_guard_cn, test=develop

* refine scope_guard_cn, test=develop

* refine, test=develop

* refine, test=develop

* modify WeightNormParamAttr doc

* modify

* modify WeightNormParamAttr

* modify

* modify

* modify

* test

* test

* test=develop

* add params declearation

* add declearation

* test

* fix Varaible doc

* fix LOD to LoD

* fix LOD to LoD

* test=develop, refine doc

* test=develop, refine doc

* refine append-backward cn

* refine in_dygraph_mode, test=develop

* refine default statements, test=develop

* add links, test=develop

* fix links, test=develop

* add blank beside links, test=develop

* refine, test=develop

* refine, test=develop

* add param_attr example

* move example

* refine code emxpale

* fix scope doc

* Polish executor doc

* refine doc for api Program, BackwardStrategy, default_start_up_program

* remove wrong binary char to make file not binary

* delete binary file and push a new file as regular one

* change name back since we delete bianry Program_cn on develop

* refine clone doc

* remove additional gitignore

* refine doc about some info

* refine doc about some info

* refine doc about some info

* refine doc about some info

* refine doc about some info

* remove useless info

* refine doc

* fix code

* fix doc error in Program_cn.rst

*  add code and refine doc

* refine clone doc

* update LoDTensor_cn.rst, test=document_preview

* update LoDTensor_cn.rst, test=document_preview

* update description of LoDTensor

* follow comments

* add fluid.embedding cn doc test=document_preview

* fix example code test=document_preview

* refine ref link

* fix param True style

* add fluid.one_hot zh doc

* refine code style

* fix dtype description

* add one_hot_cn.rst in fluid_cn

* add default value

* support LoDTensor

* modify embedding doc

* refine param_attr

* rm warning

* fix data

* add padding data update doc

* add np.dtype

Since Program_cn.rst is a Binary file we delete it first then we will add a regular rst file back

* fix docs, test=develop

* fix LoDTensor ref bug, test=develop

* follow lanxianghit's comments, test=develop

* add range of output random int tensor, test=develop

* deprecate paddle.fluid.memory_optimize

* fix comment

* fix comment