Add support for multiple Author

Problem/Motivation

Base from https://scholar.google.com/intl/en/scholar/inclusion.html#indexing multiple authors need separate metatag

<meta name="citation_author" content="Liu, Li">
<meta name="citation_author" content="Rannels, Stephen R.">
<meta name="citation_author" content="Falconieri, Mary">
<meta name="citation_author" content="Phillips, Karen S.">
<meta name="citation_author" content="Wolpert, Ellen B.">
<meta name="citation_author" content="Weaver, Timothy E.">

Proposed resolution

Change type "citation_author" to multiple