Adding requester's address information to Plug.Conn as 'peer'

I found myself needing to know the requester's ip address, rather than pulling it out with `:cowboy_req.peer` in my app, I added it to Plug. Think this'll be useful?
You can match explicitly on the port, it is defined here: https://github.com/koudelka/plug/blob/peer-address/test/plug/adapters/cowboy/conn_test.exs#L10