Used to send or accept friend requests.
URL : /friends/add/:username/
URL Parameters : username=[string]
users username.
Method : GET
Auth required : YES (Access token in request header)
Permissions required : None
Code : 200 OK
Content : "Friend request sent"
OR "Friend added"
Condition : If user does not exist.
Code : 404 Not Found
Content : "User not found"
Condition : If users are already friends.
Code : 400 Bad Request
Content : "You are already friends"
Condition : If friend request is already sent.
Code : 400 Bad Request
Content : "Friend request already sent"