use _.extend in toVinyl (for use in Verb)

Use lodash extend and support for options, to minimize [`.toVinyl` in verb](https://github.com/tunnckoCore/verb/blob/v0.3.0/index.js#L375-395) to this

```js
Verb.prototype.toVinyl = function(value, options) {
  debug('toVinyl: %j', arguments);
  var opts = extend({}, this.options, options);

  return tutil.toVinyl(value, opts);
};
```

I will also send PR and to Verb after few minutes.
Why are you extending `options` over `locals`... shouldn't those each be their own property?