This setup is counter-intuitive to most uses of an event emitter.
I would expect that I would have to register a listener to the change and rename events.

ie
```javascript
var parser = new NagiosParser(opts);
parser.on('change', changeHandler);
parser.on('rename', changeHandler);

function changeHandler(file) {
  parser.readFile(file, function(err, res) {
    console.log(res);
  });
}
```