gstreamer-gi: add convenience methods to Element

Reported by Vincent Carmona. Thanks!!!

gstreamer-gi/lib/gst.rb

@@ -33,6 +33,7 @@ def init(argv=ARGV)
       loader = Loader.new(self, argv)
       loader.load("Gst")
       require "gst/bus"
+      require "gst/element"
     end
   end
 

gstreamer-gi/lib/gst/element.rb

@@ -0,0 +1,35 @@
+# Copyright (C) 2013  Ruby-GNOME2 Project Team
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+module Gst
+  class Element
+    def stop
+      set_state(State::NULL)
+    end
+
+    def ready
+      set_state(State::READY)
+    end
+
+    def pause
+      set_state(State::PAUSE)
+    end
+
+    def play
+      set_state(State::PLAYING)
+    end
+  end
+end