Pytchat

+ Fixed bugs.
+ Removed some features (CLI, Extractor, VideoInfo).

For development environment
+ Added pipfile (pipenv).

Fix
+ Fixed missing data when converting chat list to JSON string.

Fix
+ HTMLArchiver uses temporary files to reduce memory usage.
+ Modified exception handlings when the chat stream finished.

Fix
+ Fixed test data (DefaultProcessor datetime attribute) (22)

Develop environment
+ Added GitHub workflow for automation tests. (22 : thanks for [wakamezake](https://github.com/wakamezake) )

Fix
+ Updated requirements.txt and requirements_test.txt