status: show progress when doing byte-level checks

[timmattison]

This is related to #115

Since the full status check can take a long time it would be good to have a status bar that shows how far along it is and what is being done. I have a system that has a base level of data that is 275 GB. The data was updated (went from symlinks to regular files) but the contents were still the same. When I run dud status I can see that it has read 1.06 TB from disk and isn't finished yet so it'd be good to see what's going on so I can figure out if I did something wrong and/or if I want to wait for the results or do something else.

[kevin-hanselman]

I agree, this is a good feature! I'll look into how easy it would be to implement.