Django-resized

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- Feature: optional manualy setup the extensions for image types in setting DJANGORESIZED_DEFAULT_FORMAT_EXTENSIONS.
- Feature: switch on/off normalize_rotation in setting DJANGORESIZED_DEFAULT_NORMALIZE_ROTATION.
- Fix typo in DJANGORESIZED_DEFAULT_FORCE_FORMAT settings name in code.

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- Feature: added force_format.

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- Fix: error when orientation exif data is empty.

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- Fix: add a deconstruct method.