style/app_margin library

1. tang_appbase package
2. documentation
3. style/app_margin.dart

tang_appbase package

1. Libraries
2. bloc/app_base_bloc
3. config/tang_app_config
4. style/app_margin
5. style/app_text_style
6. tang_appbase
7. widget/app_button
8. widget/app_image
9. widget/app_line
10. widget/app_navigation_bar
11. widget/app_rich_text_span
12. widget/app_scaffold
13. widget/app_text