Remove file type extension in URL that allows for content negociation

if you curl localhost:8888/users/1.xml you can get XML without passing an Accept header.

But reading more about RESTful design, I learned it goes against the URI definition, because /users/1 would be considered different from /users/1.xml.

It makes sense to me, and it was more of a gimmick to play in the browser anyway. It will simplify the code and remove some ugly hacks and dependencies on hardcoded mime types.