added GTK4 support

examples/gtk3/gaction.nim

@@ -0,0 +1,27 @@
+# https://wiki.gnome.org/HowDoI/GAction
+# nim c gaction.nim
+import gintro/[gtk, glib, gobject, gio]
+
+proc saveCb(action: SimpleAction; v: Variant) =
+  echo "saveCb"
+
+proc appActivate(app: Application) =
+  let window = newApplicationWindow(app)
+  let action = newSimpleAction("save")
+  discard action.connect("activate", saveCB)
+  window.actionMap.addAction(action)
+  let button = newButton()
+  button.label = "Save"
+  window.add(button)
+  button.setActionName("win.save")
+  var h: cstringArray = allocCstringArray(["<Control><Shift>S"])
+  setAccelsForAction(app, "win.save", h)
+  deallocCStringArray(h)
+  showAll(window)
+
+proc main =
+  let app = newApplication("org.gtk.example")
+  connect(app, "activate", appActivate)
+  discard run(app)
+
+main()