Added support for file globbing in expose property

If expose contains a files array, member objects will be passed to
grunt.file.expandMapping() to support exposing patterns of files
as simplified names/paths. Each object in the files array must
provide the cwd and src properties, while dest is optional.

For example, the following config will expose all .js files for ```require```ing within the vendor directory, at any level, simply by their filename, minus the extension.

```
expose: {
	files: [
		{
			cwd: './vendor/',
			src: ['**/*.js']
		}
	]
}
```

Adding ```dest: 'lib/'``` to the object would enable ```require("lib/somename")```