Add simple check to see if username is registered

[Nautman]

I know it's possible to use get("/user"), but I don't need to get back all information on their profile just to see if the username is available.

[kelszo]

Should this be done by sending specific error codes on registration or another route for checking username?

[Nautman]

Another route. The route doesn't need to send error codes. To be clear, this change isn't even necessary as the previous way works. But you could argue it's better.

[kelszo]

Will add this if needed in the future. One could add just a query parameter like ?fields=none that only returns true/false.

[Nautman]

That'd work perfectly.