Copter: inav circle initial implementation
Tools: removed unused/unmaintained ArduTracker

this has not compiled for a long time.
DataFlash: removed the byte and word based interfaces

simplifing ready for PX4 flash logging
AP_HAL: added HAL_BOARD_NAME define
DataFlash: make the public interface much narrower

make many variables private, to simplify interface ready for PX4
DataFlash: fixed signed/unsigned errors in API
Plane: fixes for new DataFlash API
Copter: fixes for new DataFlash API
Rover: fixes for new DataFlash API
DataFlash: added Block layer in classes

this will allow the addition of a DataFlash_File implementation of the
DataFlash API which will store logs in a traditional filesystem. That
will align better with the PX4 design, and be more useful for fast
transfer of logs to a host computer
DataFlash: added log_num to dump interface

this will be used by the file oriented logging code
Rover: always build sonar code

can use enabled/disabled parameter for runtime control
Rover: added more sonar parameters

better control over obstacle avoidance
Rover: updates for new dataflash API
Plane: updates for new dataflash API
Copter: updates for new dataflash API
DataFlash: started on file interface
Rover: removed old LITE mode

this will be replaced with a AHRS_Lite backend later
Rover: change sonar_dist to sonar_dist_cm

make units clearer
Rover: cleaned up sonar_trigger_cm parameter