Cash: ability to load config files through the magic of hashie :)

Still need to update the changelog and readme... and squash :)

how you guys like it? cc @dblock
With `Yash`, I think `format` should not be an option. It's a YAML file that supports ERB. However as a future extension maybe we can refactor Yash into something that separates the parsing and the accessing logic. So you would mixin `Yash::YamlWithERB` or something like that?