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
i've remove the format as an option.
I like the idea of moving the parser into mixing, but what about we do that in the futur? It'll then make sens to have a folder extensions/yash/yaml_with_erb_parser etc.

Or if you think about other parsers now, i could do that.