More parameters in "files" array: relative paths & '*' for globing

I'm new to FuelPHP and I used my own assets library before that.
In a similar way to Casset, I had groups and files to define.
The problem is I can't manage to setup Casset as easily because of the files array.
Here's what I would have set for my library :

```
$assets_options = array(

'js' => array(
'js_dir' => ASSETS_PATH.DS.'javascripts', // public/assets/javascripts/
'main' => array( // main group
'files' => array(
'bootstrap' => 'bootstrap.js', // located in public/assets/javascripts/bootstrap/
'jquery' => '*', // glob all files in public/assets/javascripts/jquery/
'application' => array(
'common' => '*' // glob all files in public/assets/javascripts/application/common/
)
),
'combine' => true
),
)
);
```

Can this be applied in Casset OR would be a nice feature to be implemented ?

Start by reading Casset's current files-array configuration and how it resolves asset paths. Compare the requested relative-path and '*' glob behavior with the existing configuration and any available coverage. Done means nested groups, relative paths, and directory globs work without breaking existing files arrays.

Written by the indexing model from the issue text.