Grunt-style configuration format for files

This patch is backwards compatible with the `filesSrc` property. It adds support for the files globbing/expanding/etc as described in [Configuring-tasks](https://github.com/gruntjs/grunt/wiki/Configuring-tasks).

```javascript
ghost: {
  test: {
    files: [{
      src: ['tests/ghost/**/*_test.js']
    }]
  },
}
```