[gtkmm] Customized CellRenderers

[Leandro Fanzone <leandro hasar com>]

I'm working on writing an editable ListView, much like a database table 
editing tool. I would like to implement a new CellRenderer that prevents 
users from entering letters on an integer field on the fly (instead of 
checking this after the editing was done), and also a CellRenderer for 
TreeModelColumns with a float/double value. The available documentation 
wasn't enough for me; can someone point me to an example (I'm sure this 
has been done a thousand times before) or to an outline of the steps I 
should follow?
Thank you very much.

Leandro Fanzone.