1.新增context内置变量2.修复一些问题

PublicTypes/RScriptVariables.cs

@@ -25,15 +25,14 @@ namespace Convention.RScript
                     internalData = value;
                     return;
                 }
-                internalData = Convert.ChangeType(value, type);
+                if (type == typeof(object) || type == value.GetType())
+                    internalData = value;
+                else
+                    internalData = Convert.ChangeType(value, type);
             }
         }
         private object internalData;
 
-        public RScriptVariableEntry(object data) : this()
-        {
-            this.data = data;
-        }
         public RScriptVariableEntry(Type type, object data) : this()
         {
             this.type = type;