Add Debian package (buildscript and package)

You can rebuild liquiprompt.deb by running the create_deb.sh script.

I'm not very aware of Debian packaging standards so you can improve it !

![bazinga_logo](https://f.cloud.github.com/assets/421328/320699/dee34dbc-9960-11e2-8ab3-7833f1c0b564.jpg)