* add name attribute to code-block, test=document_fix

* remove redundant labels, test=document_fix

* remove redundant labels (from upstream), test=document_fix

* more COPY-FROM (try multiple code example), test=document_fix

* empty commit, try to trigger PR-CI-build

* fix some `Examples:` format issues

* fix some ci errors

* refactor eager flags

* fix flags error when we switch from eager to dygraph

* fix ci problem

* fix ci

* fix ci

* merge develop and fix code style

* merge develop and fix code style

* fix op test error

* fix op test error

* fix op test error

* fix op test error

* fix op test error

* merge develop

* fixed docs.

* Fixed docs. test=document_fix

code bak.

fixed docs. test=document_fix

* Revert to previous version of python/paddle/fluid/backward.py

* fixed bugs.

* test=document_fix. Fixed examples.

* remove useless import. test=develop

As the title 

* Update IterableDataset API

* Update TensorDataset API

* Update APIs in paddle/text/datasets

* Update dataset.py

* add paddle.io.ComposeDataset & paddle.io.ChainDataset. test=develop

* add TensorDataset. test=develop

* add IterableDataset support in multiprocess DataLoader. test=develop

* add DataLoader, Dataset, BatchSampler