Add named exports
Add named exports

Would love to do this:

```javascript
import { Map, Record } from 'immutable';
```

but at the moment, that's not spec compliant, since immutable only exports a default object.

Thoughts? Pardon if this has been discussed before and I just missed it. Thanks!

facebook/immutable-js,facebook/immutable-js,facebook/immutable-js,facebook/immutable-js