Show the commit which removed a file

[jasoncodes]

Where the “Have a look at the repo” message is outputted, we should instead perform a git log on that file (starting at $REF, if specified) to show the commit in which the file was deleted/moved.

If the file never existed at that path, the existing behaviour should happen. The git log call should probably use options similar to --find-renames=40 --full-diff --stat --max-count=1.