Including the file in the lines behaves better when limiting with --after,
since only files that changed in the time period are shown.
Still not fully happy with the line layout, but putting the +/- first
followed by the date seems a good change.
This needs to run git log on the location log files to get at all past
versions of the file, which tends to be a bit slow.
It would be possible to make a version optimised for showing the location
logs for every key. That would only need to run git log once, so would be
faster, but it would need to process an enormous amount of data, so
would not speed up the individual file case.
In the future it would be nice to support log --format. log --json also
doesn't work right yet.
