Extend _.values to return values of the specified keys.

We can use `_.values(_.pick())` in some cases. But there are cases that values of some keys must be repeated.
The requested `_.values` accepts any combination of keys and returns their values.

```
_.values({ one: 1, two: 2 }, 'one', 'two', 'one')
// returns: [1, 2, 1]
```

For example in a context menu items list:

```
var items = {
	open: {...},
	refresh: {...},
	delete: {...},
	props: {...},
	separator: {}
};

var contextMenuItems1 = _.values(items,
	'open', 'separator', 'refresh', 'delete', 'separator', 'props' );
var contextMenuItems2 = _.values(items,
	'refresh', 'separator', 'delete', 'separator', 'props');
```

In this example we need two separate "separator"s in the context menu while `_.values(_.pick(items))` can not provide them, because `_.values(_.pick(items))` returns a unique value for the repeated key ("separator") but the suggested `_.values` returns two values for the two requested "separator"s.

Thanks.