Add support for importing specific module from directory

[gurs1kh]

Using the README.md example, it would be nice if you could do something like:

import { actionA, actionB } from './actions';

This way you could import only what you need without having to write out a separate import for each one.

[jfeldstein]

This is done by adding one asterisk to the path:

import {
  LoggedOutScreen,
  ClientsListScreen,
  ReceiptsScreen,
} from './src/screens/*';

It's in the latest examples.