Merge 0.12.1 branch into master

Is there a reason 0.12.1 hasn't been merged into the main development branch?

It's mainly a formality since many of the changes are already duplicated on master (e.g. changing :rubygems to https://rubygems.org in Gemfile). But it's a little strange that 0.12.1 doesn't appear in History.txt on master.