exceptions/not_found_exception library

1. multi_cloud_storage package
2. documentation
3. exceptions/not_found_exception.dart

multi_cloud_storage package

1. Libraries
2. cloud_storage_provider
3. dropbox_provider
4. exceptions/no_connection_exception
5. exceptions/not_found_exception
6. google_drive_provider
7. icloud_provider
8. multi_cloud_storage
9. onedrive_provider