adds new route handling

We don't really need to return anything in the body.
We can just use 200 as success and a 401 or 403 as a failure.
I would have it as a two liner:
`unless session[:user_id] == Post.find(id).user_id then halt(403) end`
`if Post.delete.zero? then halt(401) end` 
This way, we ensure that a user can only delete his or her own post.