[NPG] Supplement EM data with RIS (if we can find it)
[NPG] Tweaks to author handling, ISSN, and abstract
[NPG] Don't break when ISSN is missing
[NPG] add support for ToC
[NPG] Add more multiples. Remove check for multiple nodes so that errors get reported
Merge pull request #519 from aurimasv/nature

[NPG] Supplement EM data with RIS (if we can find it)