docs: Simplify README and add detailed documentation files

- Reduce README from 1200+ to 230 lines (cleaner, focused)
- Add docs/API_REFERENCE.md - Complete API documentation
- Add docs/BEST_PRACTICES.md - Use case patterns and recommendations
- Follow pattern of popular packages (bloc, riverpod, get_it)
- Link to detailed docs from README

README now includes:
- Quick highlights table
- Installation
- Quick start examples
- Core concepts
- v1.1.0 feature summary
- Documentation links
- Quick reference table
- Comparison table

Author: Nguyễn Tuấn Việt