Add ability to kill walkers

[TomTranter]

This type of behavior can be used to simulate NMR data https://www.sciencedirect.com/science/article/pii/S1090780707001644 Would be relatively simple to implement but would mess up the MSD calculations so needs some thought might need new metrics

[jgostick]

Maybe this could be done as a post process? I'm thinking you could either find the steps in walker's path where it hit a wall, then apply a probability of being extinguished, then finding which collision event was it's last, and ignoring the rest of the walk.

I'm not sure, but I think you could find the collisions by finding steps where the walker position did not change? Or maybe we could find all coordinates in the image that is next to the wall, and find all steps where the walker assumed one of those positions. Or, just alter the code to all note at which steps the walk hit the wall.

[TomTranter]

Wall hitting is identifiable so yeah you could definitely add another calculation to kill it or not and then record dead times as a mask or dead step then filter. Shouldn't be too hard