Add grunt task runner support (including minification)

I'm not sure what build system you prefer... but if Grunt is fine, then this pull request might be of use.

This pull request:
- sets up a basic Gruntfile
 - the most immediate benefit is having a ```dist/arc.min.js``` minified version (4.1 KB vs 9.1 KB)
 - includes jshint/tape testing support