Add PowerOn support

found in an another bravia remote project

```
Bravia.prototype.wake = function() {

  var that = this;

  arpTable.fetch(function(err, table) {
    for(var i in table) {
      if(table[i].ip === that.ip) {
        wol.wake(table[i].mac);
      }
    }
  });

};
```

it works fine at home :)
https://github.com/alanreid/bravia/blob/master/lib/index.js