this adds error checking to all operations on the compass, to ensure
that we don't accept invalid data
This also fixes the calibration values for the 5883L to match the
recommended values in the spec
git-svn-id: https://arducopter.googlecode.com/svn/trunk@2815 f9c3cf11-9bcb-44bc-f272-b75c42450872
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
tridge60@gmail.com
rmackay9@yahoo.com
james.goppert
DrZiplok@gmail.com
deweibel
jasonshort