Version 2.0.0

• Use qtpy as virtual Qt binding package. GHA unit tests are run with PySide2 and PyQt5 (#146)
• Add pyqt_env.yml and pyside_env.yml environment files (#146)
• Update CONTRIBUTING.md, README.md and add documentation file (#146)
• Refactor UISliderWidget class to support QLineEdit and layouts, update tests and examples (#168)
  • Breaks backwards compatability as UISliderWidget no longer accepts a QLabel