Combined functions to get 6 or 9 DOF

[elpiel]

Instead of reading Accel, gyro, magnetometer separately, for high-frequency needs, it would be good to have functions that return directly the 6 or 9 degrees of freedom.

Given that the registers for Accel, Gyro and Magnetometer are sequential to each other, it should be trivial to fetch those.

I'm only wondering about the API if e.g. Accel and Mag. are enabled but not the Gyro or any other combination.

Other data like Quaternion, Liner accel. gravity and temperature might also be useful in some combination, however, 6 or 9 deg. of freedom is a must at this point.