Moved +dseries/initialize.m to @dseries/initialize.m

To initialize the toolbox:

 - Add the `src` folder in the path
 - run `dseries().initialize()`

This is an Octave compatibily workaround, Octrave cannot handle
simultaneously +folder (namespace) and @folder (class).

src/+dseries/initialize.m → src/@dseries/initialize.m

-function initialize()
+function initialize(fake)
 
 % Copyright (C) 2015-2018 Dynare Team
 %
@@ -16,7 +16,7 @@ function initialize()
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
 % Get the path to the dseries toolbox.
-dseries_src_root = strrep(which('dseries.initialize'),'+dseries/initialize.m','');
+dseries_src_root = strrep(which('@dseries/initialize'),'@dseries/initialize.m','');
 
 % Check that the x13 binary is available
 nox13 = false;
@@ -65,8 +65,7 @@ if ~exist('isint','file')
 end
 
 if ~exist('isoctave','file')
-    addpath([dseries_src_root 'utilities/missing/isoctave']);
-    %p{end+1} = 'utilities/missing/isoctave';
+    p{end+1} = 'utilities/missing/isoctave';
 end
 
 if ~exist('shiftS','file')
@@ -85,7 +84,7 @@ if ~exist('ndim','file')
     p{end+1} = 'utilities/missing/ndim';
 end
 
-if ~isoctave && (~exist('rows','file') || ~exist('columns','file'))
+if ~exist('OCTAVE_VERSION') && (~exist('rows','file') || ~exist('columns','file'))
     p{end+1} = 'utilities/missing/dims';
 end
 
@@ -97,7 +96,7 @@ if ~exist('get_file_extension','file')
     p{end+1} = 'utilities/missing/get_file_extension';
 end
 
-if isoctave && ~exist('user_has_octave_forge_package','file')
+if exist('OCTAVE_VERSION') && ~exist('user_has_octave_forge_package','file')
     p{end+1} = 'utilities/missing/user_has_octave_forge_package';
 end
 

src/@dseries/subsref.m

@@ -83,6 +83,8 @@ switch S(1).type
         end
       case 'struct'
         r = dseries2struct(o);
+      case 'initialize'
+        initialize(o);
       case {'baxter_king_filter', 'baxter_king_filter_', ...
             'cumsum','cumsum_', ...
             'insert', ...