Let users log out

--verifying that users don't have the same name will be done through coffeescript with pusher
Remember that `session` is different for each user, so you can pass in `session` without keeping track of ALL sessions for ALL users.

```ruby
class RoommSession
  def initialize(session)
    @session = session
  end

  def allowed_to_access?(room)
    @session[room.id]
  end

  def leave(room)
    @session[room.id] = nil
  end
end
```