Add IMU support

[n8willis]

Currently support is missing for inertial measurement units (IMU). Roll/pitch/yaw data can be vital for offroad vehicles. In addition, IMU-provided orientation and velocity information has separate important use cases -- such as keeping the navigation map oriented correctly in the absence of GPS lock.

[tripzero]

I like your suggestion. We currently have Acceleration, but that's only part of IMU. I agree Roll/pitch/yaw support should be included.