feat(preprocessors): add's support for configuring preprocessors

this feature allow users to configure the preprocessors when setting them up on configuration, one example about where it can be useful is on Coffeescript preprocessor, to do as:

```javascript
preprocessors = {
  '**/*.coffee': {
    name: 'coffee',
    options: {bare: false}
  }
};
```

this will enable the preprocessors to accept options, making them customizable