* add new seq2seq example: rnn_search (#3574)

* re-commit seq2eq example: rnn search

* add new_seq2seq examples: rnn_search and vae_text

* modify dataset description in vae_text/README.md

* modify vae_text/README.md and vae_text/download.py

* update vae_text/infer.sh and vae_text/README.md

* add multi-gpu support for rnn_search; fix windows support for rnn_search and vae_text

* remove parallel argument in args.py

* remove hard codes

* remove hard codes

* update download.py for windows download

* fix model path for windows in vae_text/infer.py

* fix python2 utf-encoding

* fix utf-8 error in python2 when predict (#3721)

* change rnn_search to seq2seq; change vae_text to variational seq2seq (#3734)

* re-commit seq2eq example: rnn search

* add new_seq2seq examples: rnn_search and vae_text

* modify dataset description in vae_text/README.md

* modify vae_text/README.md and vae_text/download.py

* update vae_text/infer.sh and vae_text/README.md

* add multi-gpu support for rnn_search; fix windows support for rnn_search and vae_text

* remove parallel argument in args.py

* remove hard codes

* remove hard codes

* update download.py for windows download

* fix model path for windows in vae_text/infer.py

* fix python2 utf-encoding

* change rnn_search to seq2seq; change vae_text to variational seq2seq

* change rnn_search to seq2seq; change vae_text to variational seq2seq

* mv variational seq2seq to variational_seq2seq

* remove old projects (#3736)

* fix use_gpu=False error (#3775)

* update_seq2seq_readme (#3783)

fix typos for paddle dialogue, and reserve a link for PaddleMT

* Use new save/load api and change fluid.layers.data to fluid.data (#3547)

* Use new save/load api and change fluid.layers.data to fluid.data

* add check for paddle version

* Use new save/load api in ptb_lm (#3546)

* Use new save/load api in ptb_lm

* add check for paddle version

* unify reader to dataloader (#3488)

unify reader to dataloader

* Use new save/load api and change fluid.layers.data to fluid.data (#3547)

* Use new save/load api and change fluid.layers.data to fluid.data

* add check for paddle version

add link for TALL into develop, fix link for PaddleLARK in README.md

* add reciprocal links for both READMEs

* add export_model doc

* add CACascadeRCNN doc
* add pretrain model download link

use io.open instead open in rcnn/yolo/ssd

* fix the labelme2coco.py

* fix the labelme2coco.py

* add more entries to the README.md and simplifiy them; add README for DeepVoice3 in PaddleSpeech

* add a session for model in  dygraph mode, but no more details are provided now.

* update README for dygraph

* update README for PaddleNLP and fix anchor for hyperlink

* fix anchor for hyperlink

* fix typos

* Update PaddleDetection README
* Fix some link

* Rename language_representations_kit to PaddleLARK

* Update link to ernie

* Revert change in bert/train.sh

* Update PaddleDetection/README_cn.md
* Follow comments
* Small update

* Add inference benchmark
* Adjustment order
* Update some descriptions

* [metric learning] fix windows download dataset

* add windows support on language model download dataset.

* add windows support on language model download dataset.

* fix