qinduohao

支持PaddlePaddle，一起加油！

1. `ddp_equalize` seems deprecated now. Refer to [ddp_equalize #194](https://github.com/webdataset/webdataset/issues/194)、[IGNORE_test_ddp_equalize](https://github.com/webdataset/webdataset/blob/b0d03fda8bbd687c896c1910bf027bb3d0b31fb4/webdataset/tests/test_xcompat.py#L118) 2. `ddp_equalize` is also use `with_epoch` and `with_length` funtions. Refer to [ddp fixes](https://github.com/webdataset/webdataset/commit/a335e5b820c63a7819869b9971408bfd2e6db83c)