Option to dump plot into a file on every epoch

[micmarty]

It would be very useful in case jupyter closes or training cell is rerun - plots will get lost.
Please consider adding this feature or maybe tell me how could I make it without manually modifying sources.

[stared]

@micmarty There is an option to do so:

PlotLosses(fig_path="chart.png")```

or if you want to create a different one each epoch (instead of overwritting):

PlotLosses(fig_path="chart_{}.png")` ``

Vide https://github.com/stared/livelossplot/blob/master/livelossplot/generic_plot.py

Let me know if it works.