Added method converting dseries object to struct (recursively).

src/@dseries/struct.m

+function p = struct(o)
+
+% Converts dseries object to structure.
+
+% Copyright (C) 2017 Dynare Team
+%
+% This file is part of Dynare.
+%
+% Dynare is free software: you can redistribute it and/or modify
+% it under the terms of the GNU General Public License as published by
+% the Free Software Foundation, either version 3 of the License, or
+% (at your option) any later version.
+%
+% Dynare is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU General Public License
+% along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
+
+warning('off', 'MATLAB:structOnObject');
+
+p = struct(o);
+p.dates = struct(p.dates);
+
+warning('on', 'MATLAB:structOnObject');
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