Custom config passed to Ream constructor is ignored
Custom config passed to Ream constructor is ignored.

Ream constructor recently started to looks like this:

```js
class Ream extends Event {
  constructor(options, config) {
```

however `config` is always undefined there.

Steps to reproduce:

```js
const ream = require('ream')

const app = ream({ config: false }, { entry: 'xyzzy.js' })
console.log(app.config.entry) // index.js
```

On a related note, https://ream.js.org/api.html#ream-options should be updated to reflect the recent API change.