ENH: Store named tmp arrays; calculate Kalman gain
ENH: Added tmp4=F_t^{-1} H_t (will be required for smoothing)
FIX: incorrect Kalman gain after convergence.
DOC: Typo in docstring.
FIX: incorrect reduced form polynomials.
FIX: Error displaying summary dates prior to 1900
ENH: Added state and disturbance smoothers.