Refactors code into classes, adds Bundler (for easier gem management) + rubygems support, adds Rspec

Still have to write some basic specs, but the stuff is there at least, to get it started.

The rendering-as-PDF is presently showing only two cards per row -- it would be trivial to go back to doing table based code instead, but I'm really trying to get it to be div-based with floating. :)