Diff of PDF/format

• The added line is THIS COLOR.
• The deleted line is THIS COLOR.
• Go to PDF/format.

- 詳細PDF入門 ー 実装して学ぼう！PDFファイルの構造とその書き方読み方
--  http://itchyny.hatenablog.com/entry/2015/09/16/100000

- http://www.usefullcode.net/_m/01_pdf_format_spec.php