Add a simple way to extend class methods

[BravoSimone]

Right now you need to define self.prepended method and use the class passed as a parameter to override all class methods. It would be great to automatically use all methods defined in a nested module called ClassMethods to override class ones:

module Animals::Dog::AddGenus
  module ClassMethods
    def genus
      'canis'
    end
  end
end

Animals::Dog.genus #=> 'canis'