ANNOUNCE: tumbler 4.21.0 released

tumbler 4.21.0 is now available for download from
  
  https://archive.xfce.org/src/xfce/tumbler/4.21/tumbler-4.21.0.tar.xz
  https://archive.xfce.org/src/xfce/tumbler/4.21/tumbler-4.21.0.tar.xz?sha1
  https://archive.xfce.org/src/xfce/tumbler/4.21/tumbler-4.21.0.tar.xz?sha256


What is tumbler?
================

Tumbler is a D-Bus service for applications to request thumbnails for
various URI schemes and MIME types. It is an implementation of the
thumbnail management D-Bus specification described on 

  https://www.freedesktop.org/wiki/Specifications/thumbnails/

written in an object-oriented fashion using GLib and GObject. Its
modular architecture makes it very flexible and useful in many
situations. It provides plugin interfaces for extending the URI schemes
and MIME types for which thumbnails can be generated as well as

for replacing the storage backend that is used to store the thumbnails
on disk. Tumbler's functionality can also be extended via specialized
thumbnailer services implemented in accordance to the thumbnail
management D-Bus specification.

Website: 
  https://docs.xfce.org/xfce/tumbler/start


Release notes for 4.21.0
========================
[Please note that this is a development release.]

- build: Automate copyright year management
- meson-build: Function check cleanup
- build: Fix function checks
- poppler-thumbnailer: Only use embedded thumbnail if resolution
suffices
- meson-build: Use SPDX license expression
- meson-build: Update debug/optimization flag management
- autotools-build: Add missing gtkdocentities.ent.in to EXTRA_DIST
- Add meson build
- ffmpeg-thumbnailer: Bump ffmpeg version and drop CHECK_VERSION
- Set up GNU symbol visibility
- tumbler: Don't install tumbler-marshal.h
- Translation Updates:
  Albanian, Romanian, Slovak