0.2.0. Compatibility, Pandera support

Enhancements

• Add support for python 3.9
• Add support for pandas 1.2.0.
• Add support for pandera schemas via SchemaSelector.

Documentation Improvements

• Fix errors in examples.
• Clarify documentation structure
• Switch to Furo theme.

Testing improvements

• Increase coverage to 99%

Repo Improvements

• Simplify CI workflow