Calling wake should append c.out, instead of saving only last output call

[rubihouri-anzu]

https://github.com/tidwall/evio/blob/c72befaf8b4ff9419bcd8b150f582a358bebf33b/evio_unix.go#L421 should be c.out = append(c.out, out...), otherwise if calling multiple wake before loopWrite is called, only the last output is sent