Linux_HAL: Add ROS thread
Linux_HAL: Add ROS classes (wip)
More about the ROS classes
HAL_Linux: Add ROS to the Linux namespace
HAL_Linux: Include ROS library
HAL_Linux: Instantiate and initialize ROS interface
HAL_Linux: update ROS header
Fixes to cross-compile wip.

It still fails complaining about the way
ros::init() is being used.
HAL_Linux: Add args for the ros::init call
Fixes for Mac OS support
mk: Add clang for native compiling (SITL)
SITL: ROS layer first approach
Merge branch 'ros' of https://github.com/erlerobot/ardupilot into ros