Adds some Heroku specific settings to the Gemfile

Sets the ruby version to 2.0.0 in the Gemfile
Adds a commented out gem rails_12factor that should be used with deployments to environments like Heroku but on systems where assets are served up by something like nginx the way that Rails would usually expect.
Adds a local bin directory which Heroku expects when you deploy Rails 4 apps

See: https://devcenter.heroku.com/articles/rails4#upgrading-a-rails-3-app
Adds rails_12factor gem for heroku deployment
Updates verion number for assets
rails_12factor should remain commented out unless deploying to heroku
Revert "Adds rails_12factor gem for heroku deployment"

This reverts commit dcf347b370d73a4365d570ef530ef8203a078e02.
Comments out the ruby 2.0.0 statement as travis is testing 1.9.3
Updates documentation with more recent info for deploying to Heroku