extmod/modwebsocket: Add readline method.

This goes bit against websocket nature (message-based communication),
as it ignores boundaries bertween messages, but may be very practical
to do simple things with websockets.

extmod/modwebsocket.c

@@ -283,6 +283,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(websocket_close_obj, websocket_close);
 STATIC const mp_map_elem_t websocket_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_read), (mp_obj_t)&mp_stream_read_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_readinto), (mp_obj_t)&mp_stream_readinto_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readline), (mp_obj_t)&mp_stream_unbuffered_readline_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&mp_stream_write_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_ioctl), (mp_obj_t)&mp_stream_ioctl_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_close), (mp_obj_t)&websocket_close_obj },