Dataswim

Fixes and linting

- Fix tests
- Minor fixes

Many fixes

Maintenance release: start polishing:

- Refactoring: eliminate all unused stuff, stabilize the api
- Add docstrings and type annotations
- Reorganize the doc and auto-generate from the docstrings
- More tests

Maintenance release: various fixes and minor improvements

Maintenance and feature release:

- Various fixes
- Add line_num and bar_num charts for Altair