Debian packaging

This will make "debuild" just work, without adding any complexity to Tomb code. I want to make clear that this is by no means perfetct; more specifically:

* I am not sure that every dependency is included (probably not)
* I may be missing some file to install
* It would be very good to also build tomb-extras and other interesting packages, but I still have not figured how to do it. But this is a good start, I hope