def user(id, &callback)
      http(:get, "/users/#{id}.json") do |data, http|
        Firering::User.instantiate(self, data, :user, &callback)
      end
    end
def user(id, &callback)
      http(:get, "/users/#{id}.json") do |data, http|
        Firering::User.instantiate(self, data, :user, &callback)
      end
    end
returns a user by id