extensions/chess_piece library

1. chess_interface package
2. documentation
3. extensions/chess_piece.dart

chess_interface package

1. Libraries
2. arbiter/flutter_arbiter
3. chess_board_widget
4. chess_interface_dart
5. env
6. extensions/chess_piece
7. extensions/color
8. extensions/piece_color
9. models/board_theme_config
10. providers/chess_board_provider