yaml configuration to hash with indifferent access

The method #with_indifferent_access is not available at the point when the Yell is loaded with rails. 
The classes autoloads are set but the hash core extensions that adds this method into it don't.
Workaround: pass the hash through the HashWithIndifferentAccess initializer.
This resolve yell-rails gem issue https://github.com/rudionrails/yell-rails/issues/1