Support Slash Seperator for TrainResult / EvalResult for TensorBoard
🚀 Feature
TensorBoard supports and recommends grouping tags prefixed with slashes. Tags are group under the same drop down with other tags that share the prefix. For example:
step
step/train_loss
step/val_loss

epoch
epoch/train_loss
epoch/val_loss

Currently, both TrainResult and EvalResult prefix the results with an underscore (i.e. step_ and epoch_). For compatibility with TensorBoard, please support the slash separator or provide user configurable argument to set the separator.