Overview of Changes in Ruby-GTK 0.26

* Add widgets Gtk::FontSelection and Gtk::FontSelectionDialog
* The default name of the application is the ruby script filename
* Add module Gdk::Keyval which implements keyval related functions
* Fix all compiler warnings with "-Wall"
* Lots of code cleanup and refactoring
* Add a lot of missing methods
* Lots of improvements to Gtk::ItemFactory
* Rename Gtk.signal_emit_stop to Gtk.signal_emit_stop_by_name -- this
  is BACKWARDS INCOMPATIBLE (sorry). Implemented Gtk.signal_emit_stop
  properly -- this is done in the same way as GTK+ now, and makes
  more sense.
