DLPerf
Hello! I've found a performance issue in /train.py: `dataset.batch(batch)`[(here)](https://github.com/DebeshJha/2020-CBMS-DoubleU-Net/blob/82516920fabb911cc0a88af3354a179e0d0044a5/train.py#L48) shoule be called before `dataset.map(map_func=parse_data)`[(here)](https://github.com/DebeshJha/2020-CBMS-DoubleU-Net/blob/82516920fabb911cc0a88af3354a179e0d0044a5/train.py#L46), which could make your program more efficient. Here is [the tensorflow document](https://tensorflow.google.cn/guide/data_performance?hl=zh_cn#vectorized_mapping) to support it. Besides, you need to check the function `parse_data` called in `dataset.map(map_func=parse_data)` whether to be affected or not to make the changed code work properly. For example, if `parse_data` needs data with shape (x, y, z) as its input before fix, it would require data with shape (batch_size, x, y, z) after fix. Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.