WIP: First crack at gemification

I'm new to Deployinator, so perhaps I'm doing it all wrong, but the default way to deploy "a Deployinator" appears to be to fork/copy the Deployinator repo and start adding one's custom stuff right in the same tree.  This makes for a sort of guaranteed divergence situation that I really don't want to be in.

I'd much prefer to use Deployinator as a dependency (like a gem!) and introduce my custom behavior such as stacks and helpers via some kind of configuration mechanism.  I'm partial to environmental variable-based configuration, but it'd be easy enough to make that one layer and to have a ruby configuration API as well or whatever.

Again, I'm new here, so I'm willing to accept that I'm doing this all wrong.  Feedback very much appreciated :smile_cat:

**NOTE**: I realize I've played a little fast and loose with this diff, what with adding development dependencies and making things incompatible with ruby < 1.9.  This is mostly meant to be a conversation starter, and I'm happy to rebase and rework.