files in lib/serenity/ directory are not beling loaded. Looks like gemspec is broken?
ruby -e "require 'rubygems'; require 'serenity'; puts Serenity.class; puts Serenity::Generator.class"
Module
-e:1: uninitialized constant Serenity::Generator (NameError)
Fix:
s.files = Dir['lib/ * * / *.rb']