ja/Ryubook.pdf: cdda9e0 html, epub, mobi: delete "Created using Sphinx" in footer
ja/html: cdda9e0 html, epub, mobi: delete "Created using Sphinx" in footer
ja/Ryubook.epub: cdda9e0 html, epub, mobi: delete "Created using Sphinx" in footer
ja/Ryubook.mobi: cdda9e0 html, epub, mobi: delete "Created using Sphinx" in footer