Stepfile-style ruby only curriculum

This is my effort to rewrite the Ruby-focused slide deck at http://docs.railsbridge.org/workshop/ruby_for_beginners. Carina extended that slide deck for the inaugural Ruby-focused railsbridge several months ago, and I thought it would fit better in the long form. But I quickly ran out of steam, so this is somewhat incomplete: some parts may be too long, some too short. Hopefully people can get some use out of it.