v0.6.8

Gtk4 v0.6.8

Silences a warning seen on Linux when using the file dialogs.

Diff since v0.6.7

Merged pull requests:

• Use new dialogs (breaking) (#49) (@jwahlstrand)
• GtkTextView: use pointer or Ref instead of _GtkTextIter struct (breaking) (#62) (@jwahlstrand)
• improve test coverage (#70) (@jwahlstrand)