title: NPM import from subfolder
body: <p>I want to release a NPM package and I am currently looking for a solution to give users the option to use my rollup bundled ES5 code, or use the ES6 version.</p>
  <p>I have a subfolder called <code>lib</code> where I have a <code>index.js</code> and another subfolder inside it called <code>es6</code> which also has a <code>index.js</code></p>
  <p>In my <code>package.json</code> I have specified the main file as <code>./lib/index.js</code></p>
  <p>How can I now make it possible to import the ES6 file by using <code>import * as package from &quot;package/es6&quot;</code> or is that not possible at all? If not, how would you import it?</p>