Allow for multiple authors as in posterdown

Change-Id: I3152c2a2e924479df225f0f5c8a0138d9da0a50d
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index 4c568f3..12684f7 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -147,11 +147,18 @@
 <section class="title-frame" id="$idprefix$title-slide">
   <div class="author">
 $for(author)$
+$if(author.name)$
+    <span class="author">$author.name$</span>
+$else$
     <span class="author">$author$</span>
+$endif$
+  ${ sep }·
 $endfor$
     <br/>
 $for(institute)$
   <span class="institute">$institute$</h2>
+   ${ sep }·
+$endfor$
 $endfor$
   </div>
   <h1 class="title">$title$</h1>
@@ -704,7 +711,15 @@
 $include-after$
 $endfor$
 $if(theme-ids)$
-    <footer id="ids-footer"><span>$author$ · $title$ · $date$</span></footer>
+    <footer id="ids-footer"><span>
+      $for(author)$
+$if(author.name)$
+    $author.name$
+$else$
+    $author$
+$endif$
+  ${ sep }·
+$endfor$: $title$ · $date$</span></footer>
 $endif$
   </body>
 </html>