Plot training curve

Plot training curve directly from tensorboard event files.

The file structure of tb_file is like this:

.
├── dir                  
    └── map["dir"]
        └── experiment_*
            └── tb_dir
                └── events.* 

The structure of map file is like this:

[
  {
    "dir": "Algorithm1_results",
    "legend": "Algorithm1"
  },
  {
    "dir": "Algorithm2_results",
    "legend": "Algorithm2"
  }
]

The value of legend will be the depicted in the plot legend.

If you want to truncate the figure to a certain number of training dialogues on the x-axis, use the argument --max-dialogues.