Vold-Kalman filter class.
vfk = IMATVKFilter(npoles,sf)
The VOLDKALMANFILTER class is derived from the handle class. It implements the 3rd generation Vold-Kalman filter.
NPOLES is the number of poles for the filter. A higher number produces a sharper filter. If NPOLES is empty, the default of 2 will be used.
SF is the sample rate of the time histories in samples/sec.