[gtkada] Fixed-point renderer and other stuff

[Dmitry A. Kazakov]

I have updated my GtkAda contributions.

http://www.dmitry-kazakov.de/ada/gtkada_contributions.htm

Now it works with GtkAda 2.8.0. (GNAT 3.15p is OK)

A have also added a cell renderer for presentation of real numbers in
fixed-point format aligned along the decimal point. The renderer source is
used in the documentation as an example illustrating developing custom tree
view cell renderers in GtkAda.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de