* update to paddle 2.

* update readme

* upgrade multi card fintune example

* use paddle.AdamW, use grad acc

* bump propeller

* remove grad acc

* fix ner

* update propeller & distribued sample

* wip

* +seq2seq

* format

* fix erneigen

* fix pretrain

* fix static

* update propeller  for py37 compat

* fix pretrain static

* up readme

* update readme

* static pretrain

* remove optimization out of core libray

* ner use `cross_entropy`, use `ignore index`

* fix dygraph pretrain: add stop criteria

* bugfix, LN wrong initialize

* add grad acc for classifiction task

* seq2seq use fp32 when decoding

* use `paddle.io.DataLoader`

* + distill

* update readme

* update distill fig link

* propeller use vdl

* do not use pure fp16 for static graph
Co-authored-by: Nchenxuyi <work@yq01-qianmo-com-255-129-11.yq01.baidu.com>

* remove redundent dep

* + github stale.yml

* update seq2seq

* remove paddle from `requirements.txt`; add paddle version check

* rename zh/en readme