jgm/pandoc — pull request #1060 by heurist (2013-11-18 10:03:28+00:00)
Title: Epub Writer: Add cover reference to guide element

Fixes an issue with calibre http://calibre-ebook.com/ putting the
cover at the end of the book if the spine has linear="no".

Apparently this is best practice for other converters as well.

http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm#Section2.6