Django-newsletter

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- Add support for Django 3.1
- Configurable thumbnailing, dropping hard sorl-thumbnail (304).
- File attachments for messages (334).
- Drop surlex dependency improved `path()` and `re_path()` (339).
- Drop support for Django 3.0
- Add support for Django 3.2
- Add support for Python 3.10

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- Drop support for Django 1.11 LTS and Python 3.4 and 2.7.
- Updated translations.

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- Upgrade to sorl-thumbnail 12.6.2, remove install workaround.
- Update several dependencies (waitress, Django) due to security issues.

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- Support for Django Django 1.11.x (294), 2.2.x (295) and 3.0.x (296).
- Added missing migration (282).
- Update several dependencies due to security issues.
- Python 3.8 support.

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- Django 2.1 support (257).
- Python 3.7 support (256).

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- Fixed security issue allowing subscription without confirmation (108).
- Updated locales (ar, de).
- Proper default Newsletter for Message, fixes 224.
- Instructions for embedding a sign-up form (250).
- Migration issue with Django 2.0 (254).
- Miscellaneous documentation improvements.