extensions/extension_date_helper library

1. intl_date_helper package
2. documentation
3. extensions/extension_date_helper.dart

intl_date_helper package

1. Libraries
2. enums/date_range_type
3. extensions/datetime_date_extensions
4. extensions/extension_date_helper
5. extensions/string_date_extensions
6. intl_date_helper
7. utils/utils