generic position controller status/feedback message

msg/position_controller_status.msg

@@ -0,0 +1,14 @@
+uint64 timestamp		# time since system start (microseconds)
+
+float32 nav_roll
+float32 nav_pitch
+float32 nav_bearing
+
+float32 target_bearing
+float32 xtrack_error
+
+float32 wp_dist
+
+float32 acceptance_radius		# the optimal distance to a waypoint to switch to the next
+
+float32 yaw_acceptance			# NaN if not set