Receive multilines of membership event data

When members invoke many events at once, serf send multi-line messages to stdin
like following :

```sh
one.local	192.168.0.2	one	role=one,datacenter=east
two.local	192.168.0.3	two	role=two,datacenter=south
three.local	192.168.0.4	three	role=three,datacenter=west
```