[feature request] accept a function on `filter` param of `discover()` method

I would appreciate it if this product could also accept a function on `filter` param of `discover()` method.

Like this:

```javascript
mDnsSd.discover({
  name: '_googlecast._tcp.local',
  filter: (device) => {
    return device['modelName'] && device['modelName'] === 'Google Home Mini'
        && device['familyName'] && device['familyName'] === 'Living Room'
  }
});
```
