def save config_file
      config_file ||= @config_file
      File.open(config_file, 'w') do |f|
        f.puts self.to_s
      end
    end
def save config_file
      config_file ||= @config_file
      File.open(config_file, 'w') do |f|
        f.puts self.to_s
      end
    end
Saves the settings to a YAML config file. If no file is
 specified, the default location ('~/.biopsyrc') is used.