* 升级parser API和模型
* update docs: add new pages for tutorials
* upgrade CWS api download source
* add a new method for dataset field access
* add introduction for bert
* add more unit tests for api/processor
* remove unused test data. Add new test data.

* refine code style

* update fastNLP.core.rst
* refine all docstrings in core/

* remove torchvision in requirements.txt

update MLP

move example to docs

设置了模板，对fastNLP文件夹下的内容生成了文档