* 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

* rm unused ckpt and sort ckpt

* use max op idx to sort, test=develop

* remove unsed code,test=develop

* add testcase, test_develop

* modify test case, test=develop

* 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 error message for new data API

* 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

* add more checks to create_parameter test=develop

fix code example of elementwise op in en_doc

* Add input check and refine error message

* Refine test case and comments

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

test=develop

* 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

* delete debug vlog & add rpc function & fix word2vec bug & speed GEO-SGD

add executor.FetchHandler for train/infer from the dataset

Heartbeat for distributed async training.

* add error log

* Update crf_decoding api & example

test=develop

* Update api spec

test=develop

* Fix linear chain crf api

test=develop

* Avoid sharing data pointer with input

test=develop

* Simplify the logic in linear_chain_crf_decoding

* Add unittest for crf_decoding when label & path both are set

test=develop

* Update API spec

test=develop

* Add unittest for layers && correct infer_shape in chunk_eval

test=develop

* test=develop, fix docker with paddle nccl problem

* test=develop, Add Variable api and refine dygraph related API

* test=develop, Add Variable api and refine dygraph related API

* test=develop, refine test for new api and error info

* test=develop, refine error info and test_layers

* test=develop, add API.spec

* test=devleop, fix to_string python2 and python3 compat error and refien doc

* test=devleop, add API spec

* test=devleop, update API spec

* test=devleop, update API spec

* test=develop, invoke ci

* test=develop, fix example code

* test=develop, update API spec

* test=develop, fix auto_prune_error_on_leaf

* test=develop, fix auto prune error on loss stop_gradient

* test=develop, remove useless error check

* test=develop, add more ut for sorted gradient