Allow new commands to be declared

[Thelvaen]

Hello, I found your application, and I was liking some points, but, as we're using it in closed environnement, and as a support tool, we need to allow more "specific commands" that could be run (show interface, ).

I've found the way you describe new commands as inheriting from the base class kinda disturbing, hence, if you could think in a way to do it, it would be great.