Enables the connection.send/3 to respond custom http error codes using binary strings.

Hello guys!

I was working on a custom project where is needed to return custom http error codes, the problem is that the guard does not allow to pass a binary string as the status parameter, even if cowboy supports it.

```elixir
# Typical method
conn.send 404, "Wrong page bud"

# Custom http response code
conn.send "499 Wrong page bud", "Another thing"
```

If this a no go,  no explanation is required or asked for.

Thanks!