News in 6.4.0, 2023-01-01
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* Build: simplify handling of library soversion.
* Add some new API (see the reference documentation).
* Some API breaks (see the reference documentation).
* Experiments to simplify GtkStack custom switcher implementations.
  Moved the result to the attic/ directory.
* TeplView: add code from gedit: override delete_from_cursor vfunc.
  In gedit it's for the Ctrl+D keybinding to delete the current line.