Add EPUB version
Support for meta elements in metadata (EPUB 3)

http://www.idpf.org/epub/30/spec/epub30-publications.html#sec-meta-elem

A bit more liberal than what’s in the spec to account for non-compliant
EPUBs found in the wild.
Merge pull request #8 from julien-c/master

EPUB3: Support for <meta> elements in metadata