Allow for passing of custom config object

For our project [Cylon](http://cylonjs.com), we'd like to be able to provide quick/easy support for third-party PS3 controllers. We think the best way to do this is to allow users to pass in their own config objects, e.g.

```javascript
var DualShock = require("dualshock-controller"),
    config = require("./controller-config.json");
    controller = DualShock({config: config});

// do cool controller event stuff

controller.connect();
```