3.91.1 (unstable)

* Adapt to new-style enum values.
  (Murray Cumming)
* Use gtksourceview-4 instead of gtksourceview-3.0,
  and change ABI from gtksourceviewmm-3.0 to gtksourceviewmm-4.0.
  (Murray Cumming)
  https://gitlab.gnome.org/GNOME/gtksourceviewmm/issues/1 (Jeremy Bicha)
* StyleSchemeChooserWidget: Correct the underlying GType name.
  (Kip Warner) Bug #793204
* Completion:
  - Remove get/set_draw_spaces().
  - show(): Rename to start().
  (Murray Cumming)
* tests:
  - Remove Gtk::Container::show_all() calls.
  - Avoid deprecated Gtk::HBox and Gtk::VBox.
  - Use the libsigc++-3.0 syntax.
  (Murray Cumming)
* Remove deprecated API.
  (Murray Cumming)