Implement Task Dependencies

in rake you can:

``` ruby
task :foo => [:bar, :baz] do
# do stuff after :bar and :baz
end
```

In grunt you can:

``` js
grunt.registerTask('foo', ['bar', 'baz']);
```

Would love to finish that off with something like:

``` js
grunt.registerTask('foo', ['bar', 'baz'], function() {
// do stuff after 'bar' and 'baz'
});
```