Debian packaging

Hi,

This enables the raspberry-pi module for installation via the apt repository: again I've clarified the readme.

Note that I've called the module `emoncms-module-rfm12pi` to differentiate it from the python gateway, and I've removed the vestigial python script from this repo based on Jerome's feedback.

The debian installer is slightly more sophisticated and restarts the service automatically; this means that no extra steps are required to upgrade the module than just running the relevant `apt` command, and it will take care of everything.

Please add the following tag: "debian/1.0" when you have merged in. This will allow me to upload the module to apt.