updating mission is handled by the vehicle code
slows down for turns
add active at destination
remove setting of loiter start time
removes unused calc_nav_steer
add ahrs reference
add set-desired-location method
move _reached_destination member in from child
calc_lateral_acceleration args renamed and added comemnts
calc_lateral_acceleration updates _yaw_error_cd
remove calc_lateral_acceleration method with no arguments
calc_throttle updates _speed_error and becomes protected
remove unused variables from calc_throttle
calc_reduced_speed_for_turn_or_distance reworked
do not use rover throttle or rtl_complete
calc_nav_steer comment updates
remove unused update_navigation
