We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
- Add overlay video renderer "video-sink" property, so that can be set
- In create_video_sink, it returns video sink instead of always NULL
- Add new renderer_new_with_sink() API to set video sink
https://bugzilla.gnome.org/show_bug.cgi?id=776490
Expose the expose() and set_render_rectangle() methods. These are useful for
proper functioning of the video overlay in various situations and toolkits.
