added gsettings example

examples/gtk3/gsettings.nim

@@ -0,0 +1,32 @@
+# gsettings.nim -- basic use of gsettings
+# nim c gsettings.nim
+# https://blog.gtk.org/2017/05/01/first-steps-with-gsettings/
+import gintro/[gtk, glib, gobject, gio]
+
+# unused
+proc toggle(b: CheckButton) = 
+  echo b.active
+  let s = newSettings("org.gnome.Recipes")
+  discard s.setBoolean("like-nim", b.active)
+
+proc appActivate(app: Application) =
+  let window = newApplicationWindow(app)
+  window.title = "GTK3, Nim and GSettings"
+  window.defaultSize = (200, 200)
+  let b = newCheckButton()
+  b.halign = Align.center
+  b.label = "I like Nim"
+  #b.connect("toggled", toggle) # we don't need this for plain binding!
+  let s = newSettings("org.gnome.Recipes")
+  if s.getBoolean("like-nim"):
+    echo "I like Nim language"
+  `bind`(s, "like-nim", b, "active", {SettingsBindFlag.get, SettingsBindFlag.set})
+  window.add(b)
+  showAll(window)
+
+proc main =
+  let app = newApplication("org.gtk.example")
+  connect(app, "activate", appActivate)
+  discard run(app)
+
+main()