Inconsistent names in `git shortlog`

`git shortlog` (specifically talking about `git shortlog -sn`, but applies to the whole subcommand) produces a list of names based on the contributors to a Git repository. But it turns out that the output of the shortlog is very inconsistent in that sometimes it uses the username and other times the full name. This can happen even in the same repo.

This isn't a big deal on its own, but there are some external tools (like thanks.rust-lang.org) that use the output of `git shortlog` to thank contributors, and it has some cases of people going just by their first name (no surnames), or people appearing multiple times, once with their username and one with their real name.

There should be a convention established. I would personally prefer using usernames, as the huge impact of Github would mean that it's easier to go to their profile just by copy-pasting their shortlog name. Maybe add a `--realname` / `-r` flag to the command to show the real names and show usernames by default?