add_sequence_tagging_api

update bert-leveldb

fix seq2seq README.md

change bert for QA

Add comments and examples

sync with upstream

Fix seq2seq and transformer on cpu

refine README and details of bmn model

Add unit testing and doc.

fix bmn bug, data type missmatch in windows

Fix unittest for predict and evaluate

add test_metrics

add nlp pretrained models

add sentiment classification

update bert and text.py