rails/rails — pull request #8951 by bolshakov (2013-01-15 11:23:11+00:00)
Title: Allow to setup default config option using block

It works the same way as `cattr_accessor`
```ruby
class User
include ActiveSupport::Configurable
config_accessor :hair_color do
:red
end
end

user = User.new
user.hair_color # => :red
```