Update dependencies so that we support Rails 4+ only.  Neatened up Gemfiles so they only contain required lines.  Updated CHANGELOG and moved to Markdown.  Fixed deprecation warnings in specs.  Removed Rails 3.x gemfiles and Travis entries.
Merge pull request #86 from petergoldstein/feature/update_to_rails_4_+

Version 2.0.0 / Rails 4+ changes