add chmod template directive for changing file file permission

usage: {chmod, Mode, File}
where: Mode is an integer, as specified by the 'mode' field of the file_info record
       (see docs for file:write_file_info/2)

src/rebar_templater.erl

@@ -254,6 +254,14 @@ execute_template([{dir, Name} | Rest], TemplateType, TemplateName, Context, Forc
             ?ABORT("Failed while processing template instruction {dir, ~s}: ~p\n",
                    [Name, Reason])
     end;
+execute_template([{chmod, Mod, File} | Rest], TemplateType, TemplateName, Context, Force, ExistingFiles) when is_integer(Mod) ->
+    case file:change_mode(File, Mod) of
+        ok ->
+            execute_template(Rest, TemplateType, TemplateName, Context, Force, ExistingFiles);
+        {error, Reason} ->
+            ?ABORT("Failed while processing template instruction {cmod, ~b, ~s}: ~p~n",
+                   [Mod, File, Reason])
+    end;
 execute_template([{variables, _} | Rest], TemplateType, TemplateName, Context, Force, ExistingFiles) ->
     execute_template(Rest, TemplateType, TemplateName, Context, Force, ExistingFiles);
 execute_template([{file, Input, Output} | Rest], TemplateType, TemplateName, Context, Force, ExistingFiles) ->