api_service/api_exception library

1. gt_api package
2. documentation
3. api_service/api_exception.dart

gt_api package

1. Libraries
2. api_service/api_config
3. api_service/api_exception
4. api_service/api_response
5. api_service/api_service
6. api_service/api_utility
7. api_service/download_helper
8. api_service/form_data_helper
9. api_service/logger
10. api_service/network_checker
11. api_service/retry_interceptor
12. gt_api