* fix pretrain reader  encoding

* dygraph

* update bce

* fix readme

* update readme

* fix readme

* remove debug log

* remove chn example

* fix pretrain

* tokenizer can escape special token
rename mlm_bias

* update readme

* 1. MRC tasks
2. optimize truncate strategy in tokenzier
3. rename `ernie.cls_fc` to `ernie.classifyer`
4. reorg pretrain dir

* + doc string

* update readme

* Update README.md

* Update README.md

* Update README.md

* update pretrain

* Update README.md

* show gif

* update readme

* fix gif; disable save_dygrpah

* bugfix

* + save inf model
+ inference
+ distill
+ readme

* Update README.md

* + propeller server

* Update README.md

* Update README.md

* Update README.md

* + sementic analysis(another text classification)

* transformer + cache
fix tokenization bug

* update reamde; fix tokenization

* Update README.md

* Update README.md

* Add files via upload

* Update README.md

* Update README.md

* Update README.md

* infer senti analysis

* + readme header

* transformer cache has gradients

* + seq2seq

* +experimental

* reorg

* update readme

* Update README.md

* seq2seq

* + cnndm evluation scripts

* update README.md

* +zh readme

* + publish ernie gen model

* update README.md

* Update README.zh.md

* Update README.md

* Update README.zh.md

* Update README.md

* Update README.zh.md

* Update README.md

* Update README.zh.md

* Update README.md

* Update README.zh.md

* Update README.zh.md

* Add files via upload

* Update README.md

* Update README.zh.md

* Add files via upload

* release ernie-gen (#444)

* release ernie-gen

* add .meta

* del tag

* fix tag

* Add files via upload

* Update README.zh.md

* Update README.md

* Update and rename README.zh.md to README.eng.md

* Update README.eng.md

* Update README.md

* Update README.eng.md

* Update README.md

* Update README.eng.md

* Update README.md

* Update README.md

* Update README.md

* Update README.eng.md

* Update README.eng.md

* Update README.eng.md

* Update README.md

* Update README.md

* Update README.md

* Update README.md
Co-authored-by: Nkirayummy <shi.k.feng@gmail.com>
Co-authored-by: Nzhanghan <zhanghan17@baidu.com>

The current code would raise NameError instead of the expected ValueError.

flake8 testing of https://github.com/PaddlePaddle/ERNIE on Python 3.8.0

$ __flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics__
```
./propeller/paddle/train/exporter.py:86:73: F821 undefined name 'v'
                    raise ValueError('unkonw inference spec type: %s' % v)
                                                                        ^
```