Add get scan path

[ercius]

This adds a function to return the path to a counted data set using the scan_id, scan_num, and/or threshold to io.

[cjh1]

@ercius I can see the utility of this function, however, I wonder if it might be better off in another location that is more site specific. I worry about encoding distiller conventions in stempy. Maybe included inline in the notebooks? Another alternative would be to put it in a contrib directory, indicating that its not part of the stempy public interface. I am open to other options too.

[ercius]

I wonder if it might be better off in another location that is more site specific. I worry about encoding distiller conventions in stempy.

That makes sense. Im happy to move it anywhere that makes sense.

Maybe included inline in the notebooks?

I was trying to avoid this because it adds unnecessary code and looks really cluttered. Maybe that is just something to live with? It is annoying to copy this between notebooks and makes it more prone to getting out of sync across notebooks.

Another alternative would be to put it in a contrib directory, indicating that its not part of the stempy public interface.

I think that would work too. It would be a simple import in the notebooks that need it. This seems like the best trade-off to me.

[ercius]

After our recent discussion I think contrib is a great alternative. Ill update the PR.

[ercius]

@cjh1 This works in my development environment. Let me know what you think about merging it