[gtkmm] Add Gtk::Window::unset_titlebar()

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 7bcef194f3a0a35b7e4fe8e8a7694f7998183dd7
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Nov 11 18:49:39 2019 +0100

    Add Gtk::Window::unset_titlebar()
    
    Fixes #57

 gtk/src/window.ccg | 5 +++++
 gtk/src/window.hg  | 5 +++++
 2 files changed, 10 insertions(+)
---
diff --git a/gtk/src/window.ccg b/gtk/src/window.ccg
index 617c9139..04606239 100644
--- a/gtk/src/window.ccg
+++ b/gtk/src/window.ccg
@@ -190,4 +190,9 @@ void Window::unset_application()
   gtk_window_set_application(gobj(), nullptr /* See GTK+ docs */);
 }
 
+void Window::unset_titlebar()
+{
+  gtk_window_set_titlebar(gobj(), nullptr);
+}
+
 } // namespace Gtk
diff --git a/gtk/src/window.hg b/gtk/src/window.hg
index 32f8c2bc..6c18d887 100644
--- a/gtk/src/window.hg
+++ b/gtk/src/window.hg
@@ -288,6 +288,11 @@ dnl
 
   _WRAP_METHOD(void set_titlebar(Widget& titlebar), gtk_window_set_titlebar)
 
+  /** Unsets the titlebar.
+   * @see set_titlebar()
+   */
+  void unset_titlebar();
+
   _WRAP_METHOD(Widget* get_titlebar(), gtk_window_get_titlebar)
   _WRAP_METHOD(const Widget* get_titlebar() const, gtk_window_get_titlebar, constversion)