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 start the refacto to bring that to Mash, the only tradeoff is that if we want to use extend, Mash.load needs to return a Module instead of a Mash.
The quick fix would be to use another method, something like:
Twitter.extend Mash.module_load('config/settings.yml', parser: Extensions::Mash::ErbYmlParser)

Also, `extend` will just define a "settings" method on the extended class. In this case that will define the Twitter.settings to return the mash