Added/Tested callback for Picker::Countdown, Given a time in seconds, it executes
callback when seconds is equal the time given.
Moved FakeDumper from spec/picker/dumper_spec.rb to spec/support/fake_dumper.rb
Fixed lib/picker/dice.rb as it was initialising dumper object, i.e calling .new
Added Picker::Rescuer to handle raised exceptions
Added/Included module Picker::Rescuer to Picker::Countdown and instance method #rescuer to handle exception raising