Add support for DS18B20 Temperature Sensing

Please find attached a pull request which add the support for DS18B20 Temperature Sensing.

This temperature sensing is based on this tutorial : http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing/

![raspcontrol](https://f.cloud.github.com/assets/1044501/907321/ba12f888-fd2a-11e2-8d6a-1504e81a891b.png)

Regards