Added a new prior art

I have added a new entry to the prior art:

* Paper now (the tool is as much on the publication process than on the format)
  * Repo/info: https://github.com/PeerJ/paper-now
  * Sample document: http://git.macropus.org/allen-insula/ (note that the source view reveals that it relies heavily on Web Components)

Developed by the people at PeerJ (a kind of an open source spin off)

I.

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Ivan Herman, W3C
Digital Publishing Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
ORCID ID: http://orcid.org/0000-0003-0782-2704