def list(*extensions)
      all_files.keep_if do |filename|
        extensions.include?(Pathname.new(filename).extname)
      end
      all_files.reject! { |file| excluded_file?(file) }
      all_files
    end
def list(*extensions)
      all_files.keep_if do |filename|
        extensions.include?(Pathname.new(filename).extname)
      end
      all_files.reject! { |file| excluded_file?(file) }
      all_files
    end
Instantiate a FileFinder with the path to a folder
 @example
   FileFinder.new("/Users/max/src/layabout")
 @api public
 Absolute paths to all the files with the provided extensions
 @example
   FileFinder.new("/Users/max/src/layabout").list(".rb", ".coffee")
 @api public
 @return [Array<String>]