Django-imagefield

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- Fixed crashes because of image fields with ``None`` values.
- Fixed a case where an unsupported image was not detected early enough.
- Added a ``IMAGEFIELD_SILENTFAILURE`` setting for silent failure when
processing images crashes. The default value of this setting is
obviously ``False``. This is mostly useful when adding
``django-imagefield`` to a project which already has images (which may
not be processible by Pillow).
- Fixed the image verification to accept CMYK images again.
- Added Django 3.0 to the test matrix.
- Removed Python 3.4 from the test matrix.
- Ensure that ``icc_profile`` isn't passed if it is falsy. The WebP
encoder didn't like ``icc_profile=None``.
- Stopped including image fields of swapped models in ``IMAGEFIELDS``.
- Replaced ``ugettext*`` with ``gettext*``.
- Added an experimental websafe processor spec.

~~~~~~~~~~~~~~~~~~~

- **BACKWARDS INCOMPATIBLE**: Changed processing to pass additional
processors' arguments as positional arguments instead of as a single
list. This change only affects custom processors, no changes are
necessary for users of the library, except if for example you passed
arguments to processors such as ``default``, ``autorotate`` etc.
- Fixed a test to assume less about the error message for corrupt
images.
- Localize the corrupt image validation errors.
- Stopped calling the storage's ``delete()`` method for non-existing
images.
- Made the field resilient against NULL values from the database.

~~~~~~~~~~~~~~~~~~~

- Made error reporting in ``process_imagefields`` include more info.
- Made image field validation catch errors while determining the image
dimension too.
- Fixed a problem where older versions of Django didn't allow specifying
the chunk size for iterating over querysets.
- Modified django-imagefield's internals to allow changing the type and
extension of generated images by way of dynamically specifying the
processing pipeline.
- Changed the API of the ``get_image`` callable in processors to only
return the image without the context (since the context is mutable and
available already).

~~~~~~~~~~~~~~~~~~~

- Fixed a crash where unpickling image fields would fail.
- Changed ``process_imagefields`` to skip exclude model instances with
an empty image field.
- Changed the ``thumbnail`` processor to not upscale images.
- Made ``process_imagefields`` not load the whole queryset at once to
avoid massive slowdowns while determining the width and height of
images (if those fields aren't filled in yet).
- Added housekeeping options to ``process_imagefields``. The only method
implemented right now is ``--housekeep blank-on-failure`` which
empties image fields where processing fails.
- Changed ``process_imagefields`` to process items in a deterministic
order.
- Clarified the processors spec documentation a bit and added an example
how to write a processor of your own.

~~~~~~~~~~~~~~~~~~~

- Dropped support for using image fields without associated height and
width fields, because it is almost (?) always a really bad idea
performance-wise.
- Fixed a bug where processed image names on Python 2 were different
than those generated using Python 3. This bug affects only
installations still using Python 2. Rerun ``./manage.py
process_imagefields --all`` after upgrading.

~~~~~~~~~~~~~~~~~~~

- Added compatibility with Django 1.8 for prehistoric projects.
- Polished tests and docs a bit.