Pointing game need a tolerance margin option

[Sangyu-Han]

Description of the problem

• Insert a clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
• Is your feature request related to a problem? Please describe.
• Add any other context about the problem here. For example, set-up to run the example.
  Pointing game in original papar(Top-down Neural Attention by Excitation Backprop) expand ground truth region by a tolerance margin of 15 pixel, to compare different resolution saliency map methods fairly.

Description of a solution

Please refer the code from torchray:
https://github.com/facebookresearch/TorchRay/blob/master/torchray/benchmark/pointing_game.py

Minimum acceptance criteria

• Specify what is necessary for the issue to be closed.
• @mentions of the person that is apt to review these changes e.g., @annahedstroem