add a Finder::order_by(...) method

src/finder.h

@@ -967,6 +967,19 @@ public:
 	}
 
 
+	Finder<ModelClass> & order_by(const wchar_t * sql)
+	{
+		if( out_stream )
+		{
+			(*out_stream) << L" ORDER BY ";
+			(*out_stream) << sql;
+			(*out_stream) << ' ';
+		}
+
+		return *this;
+	}
+
+
 	/*
 	 * like
 	 */