setSpeedFactor sets the speed factor that adjusts the speed
  of all trajectories.
 
    The speed factor reduces the speed of all trajectories
    to the specified multiplier. For example, a speed factor
    of 0.5 would turn a 5 second trajectory into a 10 second
    trajectory.
 
    This factor gets applied to all trajectories, including
    ones that have user specified time.
 
    Example:
        % double the duration of all trajectories
        trajGen = HebiTrajectoryGenerator(kin);
        trajGen.setSpeedFactor(0.5);
 
    Values above 1.0 are supported, but may result in
    trajectories that exceed the joint limits.