Change tofloat to atof.
Log data for speed, yaw rate PI controllers.
Allow reference yaw rate to be sinusoidal.

Add arguments to set reference yaw rate to a sinusoidal signal. This is
set with the shell command:
    yr <mean> <amplitude> <frequency>
Both steer disturbance torque and yaw rate refernce have been refactored
to use refsig::Sinusoid.