Proposed new messages to replace IMU message.

[tfoote]

From https://groups.google.com/forum/#!topic/ros-sig-drivers/2NvgNBOjcFQ

Also connected to ros-infrastructure/rep#95

I'm opening this for more review and to restart the discussion.

I see that we need a few things to be implemented before this can be merged.

• [ ] homogenize this with the REP 145 proposal, ros-infrastructure/rep#95
• [ ] Implement some python methods to convert forward and backwards between the old IMU message and the trio of new messages. And a node that can used to convert each way.
• [ ] Provide an IMU transport lib (in c++ and python) that will provide the necessary synchronization helper methods to handle the parallel transport in a way that keeps things synchronized.

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/if-you-work-with-imu-data-share-sample-and-get-thanked/30203/4