Rework to use Grunt 0.4.0 files API.

Hey -

I have *no* idea if you're interested in merging this in, but I had a need for some features provided by Grunt 0.4.0's new files API. Specifically, I required the `expand` option of the files object. So I changed the main task to use that, and as a result, mucked with the way options are passed in.

These were initially "for myself" changes, but if you think it's worth pulling back into your canonical repo - as-is or with alterations - have at it!

Best,
Matt