* image segmentation with u-net notebook

* update segmentation notebook

initialize paddle2.0_docs directory

* update develop readme

* update readme

* -1->None (#823)

* unify paddle 1.6 api in understand_sentiment (#824)


* unify paddle 1.6 api in understand_sentiment

* Upgrade w2v & srl's api (#828)

* Upgrade w2v & srl's api

* Upgrade label semantic roles api

* Rewrite 08.machine_translation using Paddle-1.6 apis. (#826)

* Rewrite 08.machine_translation using Paddle-1.6 apis.

* Delete the old train.py in 08.machine_translation

* Update train.py to seq2seq.py in README_cn 08.machine_translation.

* Fix the print content of seq2seq.py.

* Update code format in README_cn of 08.machine_translation.

* add 1.6 requirement (#830)

* fix bugs in Readme.md of 04 and 07 (#831) (#832)

* Polish optimizer name in 04.word2vec (#841) (#842)

* change opt name in word2vec

* update index.cn.html

* Cherry pick for paddle 1.6 (#843)
Co-authored-by: Nceci3 <ceci3@users.noreply.github.com>
Co-authored-by: NLi Fuchen <lfchener@outlook.com>
Co-authored-by: NYibing Liu <liuyibing01@baidu.com>
Co-authored-by: NGuo Sheng <whucsgs@163.com>
Co-authored-by: Nruri <shipeng1108@163.com>
Co-authored-by: NChen Weihang <sunny_cwh@163.com>

* change opt name in word2vec

* update index.cn.html

* fix dead link for book

* replace simple_img_conv_pool to conv_pool

* fix typo:Infererence

* fix predict bug in ic

revert 03 image classification: fluid.layers.data->fluid.data

* Revert "change -1 to None in data's shape (#819)"

This reverts commit 77fe59e5.

* Revert "Upgrade API using paddle 1.6 (#813)"

This reverts commit 900ba733.

This reverts commit db3cdc05.

This reverts commit adcdb7b8.

This reverts commit 104c4078.

* change layers.data to fluid.data
* change layers.embedding to fluid.embedding

* fix typo:Infererence

* fix data api

* Modify the formula of lstm

* Update README.cn.md

* Update README.cn.md

* Unify 1.6 api in 06.understand_sentiment

* fix a bug in README.md

* Update README.cn.md

* Modify the formula of lstm

Fixed issue with train_dyn_rnn.py training report nan

update coding_guideline

* fix reader

* update readme

Modified the bug in understand_sentiment
icafe : http://newicafe.baidu.com/issue/76263402/show?cid=5&spaceId=23205&from=email&noticeStatistics=23969354

fix : http://newicafe.baidu.com:80/issue/DLTP-1929/show?from=page， fix book code is not compatible with python3

Modify the code to support python3: fix problem in book05 doc and code