* test=document_fix
Fix english doc api, invloves the op of greater_equal,greater_than,less_equal,not_equal,
rank,rsqrt,diag,linspace,reduce_all,reduce_any,sign,where,zeros_like,unique_with_counts.

* Fix some format problem in the op of sign and greather_than.
test=develop
test=document_fix

* Fix the example of zeros_like, and update api.spec
test=develop
test=document_fix

* add new save load interface; test=develop

* add new save interface; test=develop

* add save load interface ;

* fix save load error;

* fix dygraph set dict bug;

* add save load unit test; test=develop

* fix test_imperative_optimizer bug; test=develop

* fix unitest optimizer bug; test=develop

* fix code coverage; test=develop

* fix converage; test=develop

* add document for apis; test=develop

* fix unitest error; test=develop

* fix save load unit test error; test=develop

* fix error message; test=develop

* change set_parameter set_optimizer to save_dygraph; test=develop

* add load_graph check; test=develop

* fix api spec; test=develop

* test=develop, fix docker with paddle nccl problem

* test=develop, refine en_doc for Variable and Program

* test=document_fix, fix English doc for Variable and Program

* test=document_fix, refine astype code block style

* test=document_fix, add example code for Variable properties

* polish en api,test=develop,test=document_fix

* modified api.spec, test=develop,test=document_fix

* modified ops for arc,test=develop,test=document_fix

* update for 1.6, test=develop,test=document_fix

* update API.spec

* Update API.spec

test=develop,test=document_fix

* Update API.spec

test=develop,test=document_fix

* refine Normal Uniform documnet

* Polish en doc of LoDTensorArray, test=develop, test=document_fix

* follow comments, test=develop, test=document_dix

* fix fluid.data code example, test=develop, test=document_preview, test=document_fix

* improve the docs of load_inference_model&load_params&load_persistables&chain.

* polish executor doc
test=develop

* fix en_doc of one-hot and embedding test=develop, test=document_fix

* modify into fluid.data test=develop, test=document_fix

* modify api.spec test=develop, test=document_fix

* fix api.spec conflict, test=develop, test=document_fix

* polish minimize en doc

* polish adam optimizer en doc

* polish adamax optimizer en doc

* polish adagrad and decayed adagrad optimizer en doc

* polish model average en doc, test=develop, test=document_fix, test=document_preview

* self review and further polishing doc

* update API.spec, test=develop, test=document_fix

* update fluid.data api in examples, test=develop, test=document_fix

* update fluid.data inferface, test=develop, test=document_fix

* replace -1 by none, test=document_fix

* polish append_backward, test=document_fix

* test=document_fix, test=develop

* test=document_fix, test=develop

* polish append_backward, test=document_fix, test=develop

* fix fluid.data code example, test=develop, test=document_preview, test=document_fix

* use None instead of -1 in shape, test=develop, test=document_preview, test=document_fix

* fix CUDA CPU places, test=document_fix, test=develop

* fix CUDAPlace param doc, test=document_fix, test=develop

* fix CUDAPlace param doc, test=document_fix, test=develop

* test=develop,test=document_preview, test=document_fix

* test=develop,test=document_preview, test=document_fix

* fix API.spec, test=develop,test=document_preview, test=document_fix

* test=develop,test=document_fix,fix transpiler doc,add API.spec

* update api example, test=develop, test=document_fix

* fix cvm and DataFeedDesc apis test=develop test=document_preview test=document_fix

* add ref and rst tensor type test=develop test=document_preview test=document_fix

* change API.spec test=develop test=ducument_fix

* fix fluid.data test=develop test=document_preview test=document_fix

* change API.spec test=develop test=document_preview test=document_fix

* fix cvm example test=develop test=document_preview test=document_fix

* change API.spec test=develop test=document_preview test=document_fix

* fix cvm example test=develop test=document_fix

* fix cvm example test=develop test=document_fix

* change api.spec example test=develop test=document_fix

test=develop
test=document_fix

* refine seq_pool/reshape/reverse test=develop, test=document_fix

* modify api.spec test=develop, test=document_fix

* fix api 1.6 doc bpr, data_norm teacher_student

* polish in_dygraph_mode, test=document_fix

* test=document_fix, test=develop

* test=document_fix, test=develop

fix code example of elementwise op in en_doc

* test=develop
Add input type and dtype check for sign_op.

* test=develop
Fix the api text format in sign op.

* test=develop
Fix the api examples in sign op add update the api.spec.

* fix APIs,test=develop,test=document_fix

* fix conflict, test=develop, test=document_fix

* fix confict, test=develop, test=document_fix

* fix confict, test=develop, test=document_fix

* fix API.spec, test=develop, test=document_fix

* change fluid.layers.data to fluid.data,test=develop, test=document_fix

* fix bug on example code, test=develop, test=document_fix

* fix API.spec,  test=develop, test=document_fix

* refine fc/seq_conv/seq_concat en doc test=develop, test=document_fix

* modify into fluid.data test=develop, test=document_fix

* update en doc

* fix doc, test=document_fix test=document_preview