* Removed a ton of code we don't need from that driver, which should make writing new drivers easier.
this will allow an airspeed sensor object to be passed to AHRS for dead reckoning
this also adds a healthy attribute, and error checking on all I2C calls
Most of the compass functionality is now abstracted in a base class, with the various sub-classes implementing just their unique functionality. git-svn-id: https://arducopter.googlecode.com/svn/trunk@1647 f9c3cf11-9bcb-44bc-f272-b75c42450872
Pat Hickey
Andrew Tridgell
DrZiplok@gmail.com