Preview-generator

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:warning: Support for python<3.6 is deprecated.

Misc
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- Remove pillow and imconvert builders
- Drop support for python3.6
- Document issue with old version of libreoffice for spreadsheet 296
- Enhanced the test cases for xcf files

Fixed issues
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- fix aspec ratio issue: https://github.com/algoo/preview-generator/issues/293

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:warning: This release introduce many changes with two of the basic builders changed (image, pdf) and a new one added (raw).

Features
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- new Image builder based on Wand (which by the way deprecates Pillow and Imagemagick command line builders): 253
- WebP image format support added to the new Wand builder: 273
- new PDF builder based on poppler-utils (which replace old PDF builder): 192
- new RAW image builder using rawpy: 249

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Fixed issues
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- Repair loading builders without pytest and make code more explicit/safe about such issue: 47517e5dd2b153f3d541fa95f7e0121a3540a041


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Fixed issues
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- enforce office mimetypes supported by LibreOffice to avoid unknown mimetype issues related to system specific configuration: 283

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Fixed issues
~~~~~~~~~~~~~

- fix issue with inkscape builder as required: 263

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Fixed issues
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- add compatibility with inkscape v1: 263

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