endpoint for getting users.
200 OK if the user exists and
404 NOT FOUND if it doesn't.
returns the user if found. the user has to have a public profile enabled for it to be fetched through the api.
returned JSON body:
|_id||string||id of the user|
|username||string||username of the user|
|avatarUrl||string||url of their avatar image|
|defaultLang||string||the default language|
|publicProfile||bool||if they have a public profile|
|supporterLength||uint||how long has the user been a supporter for, 0 if not a supporter|
|contributor||bool||if the user is a contributor to pastemyst|