Added a Gruntfile to enable building a complete file with r.js. Fixes #591

Hi!

I thought I'd give a (very) quick whack at this. It seems to work fairly well. Quite a few tests fails, but I haven't looked at why.

I spent like 30 minutes on this (new to Grunt), so it's probably possible to do it better and more cleanly than this. but it's a start at least, and I have no problem tweaking it before a possible merge