Add IP command and TIMING-MARK option to fix issue #1

So it looks like hitting CTRL-C (in Linux 3.2.0, in my case) sends two commands:
```
IAC IP             (ff f4)
IAC DO TIMING-MARK (ff fd 06)
```
I've associated two functions to work the IP command and the TIMING-MARK option so it at the very least doesn't crash. The following code should all work when you hit CTRL-C:

```js
var telnet = require('telnet');
telnet.createServer(function(client) {
    console.log('CLIENT CONNECTED');
    client.write('hello!\n');
    client.pipe(client);
    
    client.on('ip',function() {
        console.log('INTERRUPT PROCESS');
        client.end();
    });
    
    client.on('timing mark', function() {
        console.log('TIMING-MARK');
    });
    
    client.on('end',function() {
        console.log('CLIENT DISCONNECTED');
    });
}).listen(9999);
```

A few things worth noting:
 - I implemented the IP command the same way as the IAC. This is a bit of repeated code, I don't know if someone would like to generalize that, or really even if that is correct in the first place.
 - I'm not sure that the ```'ip'``` event lines up exactly with your design. Let me know if this is an issue.
 - Using a telnet client in windows does not cause the 'ip' nor the 'timing mark' events to emit. (I'm sure you figured that out by now, but still worth stating explicitly)

Hopefully this is fixes #1 to satisfaction.