FIX: State covariance shape.
REF: Improved compatibility with subclassing.
REF: nendog, nstates ... -> k_endog, k_states ...
FIX: Segfault if state covariance matrix is zeros
FIX: Incorrect loglikelihood in multivariate case
FIX: Incorrect variable in determinant calc.
DOC: Typo
ENH: Added check for zero-dim states.
FIX: incorrect dimensions exception message
ENH: Allowed setting initial variance for
approximate diffuse initialization
ENH: Made the best prefix and type available as
properties.
ENH: Added initialization to results.
ENH: Added companion matrix and differencing tools
REF: Renamed constraint tools.
ENH: Allow *args in model score, Hessian
ENH: Except on non-singular, non-pos-def matrices
ENH: Add prediction to results, cleanup, fixes
ENH: Added generic statespace model; SARIMAX model
CLEAN: Removed obsolete Kalman filter code.