Compatibility breaks
* Add `EncodeStatistics` and refactor `FFmpeg.encode()`
Minor compatibility breaks
* Merge `django.template` tags & filters into 1 file
* Split `FFmpeg` class to `FFmpeg` + `FFprobe` classes
Features
* Add module `django.exceptions`
* Add `static_abspath` Django template tag
* Add class `django.forms.mixins.EnctypeMixin`
* Add class `django.models.mixins.AlwaysUpdateFieldsMixin`
* Add class `django.models.mixins.AutoForceInsertMixin`
* Add class `django.models.mixins.AutoUpdateFieldsMixin`
* Add class `django.models.mixins.MapUniqueTogetherIntegrityErrorToValidationErrorMixin`
* Add class `django.models.mixins.RelatedModelMixin`
* Add class `django.models.mixins.UpdatePreconditionsMixin`
* Add class `django.storage.ExpressTemporaryFileMixin`
* Add class `django.test.mixins.FormWizardMixin`
* Add class `django.views.mixins.InitialMixin`
* Add class `logging.ColorizeFilter`
* Add function `collections.flatten_dict`
* Add function `datetime.multiply_time`
Fixes and enhancements
* Avoid hardcoding `\n`
* Module `console`: Write to given stream
* Module `datetime`: Make API more consistent
* Module `multimedia.ffmpeg`:
* Split `FFmpeg` class in `FFmpeg` and `FFprobe`
* Add `EncodeState` & `EncodeStatistics` classes
* Do some analysis before launching `ffmpeg` subprocess
* Fix progress if sub-clipping
* Improve handling of `media` argument
* Miscellaneous improvements
* Module `subprocess`: Import Popen from psutil if available
* Refactor function `django.signals.create_site`