Allow an easier usage on selected option of select tag

This allow us to write some easier select tag with an option selected like
```javascript
var filter = 'example';
select({name: 'filter', selected: filter},
  option({value: ''}, "All"),
  option({value: 'example'}, "Example"),
  option({value: 'private'}, "Private")
)
```

or

```javascript
select({name: 'filter'},
  option({value: ''}, "All"),
  option({value: 'example', selected: true}, "Example"),
  option({value: 'private'}, "Private")
)
```