Load levelling scheduler - first attempt
AP_Math: added quaternion normalization
AP_NavEKF: use quaternion normalize and cleanup sqrt calls
AP_Math: inline VectorN code
AP_Airspeed: added last_update_ms() interface
AP_AHRS: added get_airspeed() interface to AHRS
AP_NavEKF: use float arrays when not doing bounds checking

g++ is doing a lousy job of inlining VectorN, so avoid it when we
don't need bounds checking for production code