title: multiple authors and subtitles in Rmarkdown yaml
body: <p>I'm trying to follow <a href="http://johnmacfarlane.net/pandoc/demo/example9/pandocs-markdown.html#yaml-metadata-block">this pandoc example</a> to add multiple authors to an Rmarkdown file in the <a href="http://rmarkdown.rstudio.com/authoring_pandoc_markdown.html#yaml-metadata-block">yaml metadata block</a>. The pdf will generate in RStudio (Version 0.98.932), but there is no author information. </p>
  
  <pre><code>---
  title:  'This is the title: it contains a colon'
  author:
  - name: Author One
    affiliation: University of Somewhere
  - name: Author Two
    affiliation: University of Nowhere
  date: "`r format(Sys.time(), '%d %B %Y')`"
  tags: [nothing, nothingness]
  abstract: |
    This is the abstract.
  
    It consists of two paragraphs.
  output: pdf_document
  ---
  </code></pre>
  
  <p>I'd also like to customize the heading a bit more and add a subtitle. Possible?</p>