Qna-builder

- Fix bug in caching knowledge base
- Drop support for Haversine distance
- Add unit tests
- Reformat the code
- Minor improvements

- Update the default knowledge base to a new version v0.0.3

- Change package name to `qna-builder`
- Minor changes and improvements

- Heavily restructured the project
- Improved main classes and their method to be more readable and maintainable
- Used informative docstring for class properties
- Add enum classes for embedding models and similarity metrics
- Used Microsoft's chit-chat dataset as the default knowledge base
- Fix bugs and improve design and functionality in the knowledge base editor
- Major bug fixing and improvement across the package