LOK ABI changes

[Pranav Kant]

While playing with LOK via LOKDocView, I was wondering maybe it would
be better to add some padding to LOK class to avoid breaking the ABI,
and help for future expansion.

I am not sure about this, I saw this in some of the widget
implementations in gtk.git[1]. Any comments would be helpful

[1] https://git.gnome.org/browse/gtk+/tree/gtk/gtkwidget.h#n608

-- 
Regards,
Pranav Kant
http://pranavk.me