 Docs: GenEvent.add_handler/3 docs do not mention about using {HandlerModule, id}

If you want to use the same module as a event handler you need to pass it in as {Module, id}.  

http://elixir-lang.org/docs/v1.0/elixir/GenEvent.html <- docs

https://github.com/elixir-lang/elixir/blob/v1.0.5/lib/elixir/lib/gen_event.ex#L738 <- where this is possible.
