smoothing — Kalman smoother
[betas,sigmas]=smoothing(F,betat,betaf,sigmat,sigmaf, begsmooth)
F = transition matrix
betat = vector of filtered beta at date t with the information available at date t (beta(t|t))
betaf = vector of filtered beta at date t with the information available at date t-1 (beta(t|t-1)
sigmat = vector of filtered variances at date t with the information available at date t (sigma(t|t))
sigmat = vector of filtered variances at date t with the information available at date t-1 (sigma(t|t-1))
begsmooth = first observation where to calculate smoothed values
betas = vector of smoothed beta at date t with the information available at date T (beta(t|T)
sigmat = vector of smoothed variances at date t with the information available at date T (sigma(t|T))