Fetch options from .esformatter

Fetch options from `.esformatter` file using `esformatter.rc([filePath], [customOptions])`.
after v0.3.1 setting `preset` or `root: true` will bypass the `rc` file lookup and just return the `customOptions`, maybe change this test to:

```js
var stream = esformatter({
  whiteSpace: {
    before: {
      "ArrayExpressionClosing" : 1
    },
    after: {
      "ArrayExpressionOpening" : 1
    }
  }
});
```

this should be enough to check if custom options are being respected.