Add Gyroscope

* Some of the angle integration is inspired from [here](http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16_19&products_id=180). I have to normalize the angle to represent `360` to `0` and settle on a method for integration. Once I do that I'll inline some references in the comments.
* Part of this PR is illustrative. There's a lot of unnecessary code copying here which will be resolved once we can treat both the accelerometer and the gyro as members of a sensor class. 
* Eventually (before Nodebots Day) the gyro and the accelerometer will be integrated to expose a single orientation API. At which point we can talk about whether or not we still want to expose axis change events for single sensors.