New api

Changed the structure so that it is more semantic. Now you build a select component like this:

```javascript
<Choice.Select>
  <Choice.Option value="foo">Foo</Choice.Option>
  <Choice.Option value="bar">Bar</Choice.Option>
</Choice.Select>
```

```javascript
<Choice.SelectMultiple>
  <Choice.Option value="foo">Foo</Choice.Option>
  <Choice.Option value="bar">Bar</Choice.Option>
</Choice.SelectMultiple>
```