A thin wrapper around https://github.com/hakimel/Ladda .
If you copy files from the interwebs into your project, kittens die.
Do this instead (in your Gemfile):
gem "ladda-rails", :git => "git://github.com/Promptus/ladda-rails.git"
And, in your application.js and application.css:
//= require "spin"
//= require "ladda"
//= require "ladda.jquery" // only when you use jQuery already, see Ladda docs for usage
*= require ladda
*= require ladda-theme // this is optional - when you leave this out, it's equivalent to the "ladda-themeless.min.css from the Ladda project
We'll try to keep this project's version numbers the same as those from Ladda.