* add csc task.
1. add detection labels in convert_example

* add train progress

* rename spelling_correction to text_correction

* add pinyin vocab

* fix read_test

* fix decode

* change data.py to utils.py

* add evaluate for csc

* add parse decode for predict

* add Chinses Spelling Correction datasets

* use load_dataset('csc') instead of load_dataset(local_file)

* fix word length

* add predict script

* decouple csc model and ernie-gram

* add ernie backbone

* change default model_type to ernie

* add roberta

* fix decode

* add sighan test dataset;add sighan predict script;

* remove sighan testset

* add download script

* add README.md

* add export model

* add ernie-csc directory

* fix some review comments

* add sighan dataaset

* remove unnecessary model

* add deploy model

* add dataset download

* remove deploy/predict.py;fix some readme bug

* modify accroding to review comments

* Add more comments on model implementation

* upgrade sighan_evaluate.py

* add some comments in sighan metrics.