* move coupletdataset to paddlenlp.dataset

* move coupletdataset to paddlenlp.dataset

* add doc for coupletdataset copyright, fix other api's sample code

* support pad seq and bsz multi

* alter vocab size

* alter md5sum

* root for reader

* fix delimiter

* fix translation dataset and simplify transformer reader

* fix translation.py bugs

* delete useless comments

* set couplet download root None

* add couplet

* simplify model code

* simplify code

* update couplet README

* add pad_token to TranslationDataset, update CoupletDataset

* update couplet url, add couplet generation example

* update TranslationDataset

* upadte classname to self in __init__

* update README.md

* update SamplerHelper.batch

* update batch_size, delete a useless log

* update SamplerHelper.batch

* update SamplerHelper.batch, change cmp_fn arg to key

* Update TranslationDataset and IWSLT

* fix doc error

* update lrscheduler

* minor fix

* add pre-commit

* minor fix

* Add __len__ to squad dataset

* minor fix

* Add dureader robust prototype

* dataset implement

* minor fix

* fix var name

* add dureader-yesno train script and dataset

* add readme and fix md5sum

* integrete dureader datasets

* change var names: segment to mode, root to data_file

* minor fix

* update var name