Fixing url backslashes + Prettifying JSON + Added exclude : [path/, ...]

__Fixing url backslashes__
- path.join in windows seems to convert all fordslashes into backslashes, regulating to the system path structure.

__Prettifying JSON__
- Tests were prettified but stopped working, simple patch.

__Added exclude : [path/, ...]__
 - Grunt-tree doesn't support "Building the files object dynamically". So in return excluding files was not available.

```
//To exclude any directory or path, simply add an array of URIs:
options : {
    exclude : [
        'css/style.css',
        'img/',
        'js/bootstrap/secret.js' ]
}
```

*Note: All paths are relative to the "current directory" / "cwd"*