module Kramdown::Utils::Configurable

def configurable(name)

the data as argument or by using a block.
add_(ext_name, data=nil, &block):: Define an extension +ext_name+ by specifying either

(ext_name):: Return the configured extension +ext_name+.

object.
configurables:: Returns a hash of hashes that is used to store all configurables of the

extension:
Three methods will be defined on the calling object which allow to use this configurable

Create a new configurable extension called +name+. 
def configurable(name)
  unless respond_to?(:configurables)
    singleton_class.send(:define_method, :configurables) do
      @_configurables ||= Hash.new {|h, k| h[k] = {} }
    end
  end
  singleton_class.send(:define_method, name) do |data|
    configurables[name][data]
  end
  singleton_class.send(:define_method, "add_#{name}".intern) do |data, *args, &block|
    configurables[name][data] = args.first || block
  end
end