[FYI] unix-echo-server example does not work like you've intended

https://github.com/coolaj86/libev-examples/blob/master/src/unix-echo-server.c#L64-L67

In this case, send() call does not always guarantee to send "n" bytes because cliend->fd is non-blocking mode. 
So keeping the buffer (str[]) is needed until all buffer contents are flushed out.
