class Middleman::Configuration::ConfigurationManager

def define_setting(key, default=nil, description=nil)
  raise "Setting #{key} doesn't exist" if @finalized
  raise "Setting #{key} already defined" if @settings.has_key?(key)
  raise "Setting key must be a Symbol" unless key.is_a? Symbol
  @settings[key] = ConfigSetting.new(key, default, description)
end