configure.ac: Depends on GTK+3
gtkgl/gdkgl: Port to GTK+3
Remove GdkFont related API
Remove GdkPixmap related API
Remove deprecated API
gtkgl/gtkglarea.c: GtkObject doesnt exist anymore
examples/zktor.c: Replace GDK_<keyname> with GDK_KEY_<keyname>
examples: Do not use gtk_quit_add_destroy()
gtkgl/gtkglarea.c: Colormaps doesnt exist anymore
examples/viewlw.c: Replace the use of gtk_object_* api
examples: In GTK+3 "expose_event" is now "draw" signal
examples: replace use of deprecated gdk_window_get_pointer()
examples: replace deprecated gtk_vbox_new() function
Change .pc file

As we are breaking API compatibility
configure.ac: change libtool version to C+1:0:0

As binary compatibility has been broken
configure.ac: Set version to 3.0
gtkglglarea: Change namespace from gtk_gl_area to ggla_widget

gtkglarea is overloading the GDK and GTK namespaces; this means that
if we get a GdkGLContext in GTK+ in the future, and people link
gtkglarea with gtk, they'll have a bad time
gdkgl: Change namespace from gdk_gl_ to ggla_

gtkglarea is overloading the GDK and GTK namespaces; this means that
if we get a GdkGLContext in GTK+ in the future, and people link
gtkglarea with gtk, they'll have a bad time
examples: Port to new name space
docs: Change docs to new namespace