Previously we just expected 'title', 'subtitle', 'author', 'date'.
Now we still support those, but also support the format recommended
for epub metadata in the pandoc README:
---
title:
- type: main
text: My Book
- type: subtitle
text: An investigation of metadata
creator:
- role: author
text: John Smith
- role: editor
text: Sarah Jones
identifier:
- scheme: DOI
text: doi:10.234234.234/33
publisher: My Press
rights: (c) 2007 John Smith, CC BY-NC
...
