Move contents of gemspec to Gemfile
Mention compiling with --binstubs flag (because of Procfile)
Use bundler instead of gemfile in Rakefile
Remove integration tests as they are not needed (tests passing)
Remove fixtures as they were needed for integration tests only
Remove rubygems plugin
Remove geminabox client
Remove unexisting task from Rakefile
Leave only 2.0.0 ruby version in .travis.yml
Rename gem to rails-assets