Add ar option to estimation

Closes: #276

doc/dynare.texi

@@ -4201,7 +4201,8 @@ model. Default: @code{4}.
 distribution of the theoretical moments of the endogenous
 variables. Results are stored in
 @code{oo_.PosteriorTheoreticalMoments} (see below for a description of
-this variable)
+this variable). The number of lags in the autocorrelation function is
+controlled by the @code{ar} option.
 
 @item conditional_variance_decomposition = @var{INTEGER}
 See below.
@@ -4390,6 +4391,9 @@ Triggers estimation with analytic gradient. The final hessian is also
 computed analytically. Only works for stationary models without
 missing observations.
 
+@item ar = @var{INTEGER}
+@xref{ar}. Only useful in conjuction with option @code{moments_varendo}.
+
 @end table
 
 @customhead{Note}

preprocessor/DynareBison.yy

@@ -1521,6 +1521,7 @@ estimation_options : o_datafile
                    | o_dr_logarithmic_reduction_tol
                    | o_dr_logarithmic_reduction_maxiter
                    | o_analytic_derivation
+                   | o_ar
                    ;
 
 list_optim_option : QUOTED_STRING COMMA QUOTED_STRING