* make audio requirements optional
* add changelog for version v0.2
* add numpy constraint for compatibility with tensorflow1.15
* update faq
* fix nlp requiring tensorflow
* add torchvision to multimodal dependency
* bump version from 0.2.1 to 0.2.2
* add warning msg when tensorflow is not installed
Link: https://code.alibaba-inc.com/Ali-MaaS/MaaS-lib/codereview/9268278
* add trainer interface
* add trainer script
* add model init support for pipelineadd pipeline tutorial and fix bugs
* add text classification evaluation to maas lib
* add quickstart and prepare env doc
* relax requirements for torch and sentencepiece
* merge release/0.1 and fix conflict
* modelhub support for model and pipeline
Link: https://code.alibaba-inc.com/Ali-MaaS/MaaS-lib/codereview/8868339