added GTK4 support

examples/gtk3/listview.nim

@@ -89,9 +89,9 @@ proc appActivate(app: Application) =
   window.add(vbox)
   initList(list)
   let selection = getSelection(list)
-  connect(add, "clicked", listview.appendItem, entry)
-  connect(remove, "clicked", listview.removeItem, selection)
-  connect(removeAll, "clicked", listview.onRemoveAll, selection)
+  connect(add, "clicked", appendItem, entry)
+  connect(remove, "clicked", removeItem, selection)
+  connect(removeAll, "clicked", onRemoveAll, selection)
   showAll(window)
 
 proc main =

examples/gtk4/app0.nim

@@ -0,0 +1,16 @@
+# app0.nim -- minimal application style example
+# nim c app0.nim
+import gintro/[gtk4, glib, gobject, gio]
+
+proc appActivate(app: Application) =
+  let window = newApplicationWindow(app)
+  window.title = "GTK3 & Nim"
+  window.defaultSize = (200, 200)
+  show(window)
+
+proc main =
+  let app = newApplication("org.gtk.example")
+  connect(app, "activate", appActivate)
+  discard run(app)
+
+main()