logging issue

[ikki407]

The outputs of this library are not simple to understand if many models are trained together. So logging of information for trained models is needed to understand easily.

Like:

Level 1:

Model1 train-loss 0.5123±0.10 validation-loss 0.6345±0.15
Model2 train-loss 0.4324±0.20 validation-loss 0.5456±0.08
Model3 train-loss 0.5963±0.14 validation-loss 0.6501±0.05
...

Level 2:
...