Allow affiliation.address instead of institute

as in posterdown

Change-Id: I3ecb8e91acbdf0ee5247a1962d6236fb566e955d
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index 12684f7..8910fb5 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -159,6 +159,9 @@
   <span class="institute">$institute$</h2>
    ${ sep }·
 $endfor$
+$for(affiliation)$
+  <span class="institute">$affiliation.address$</h2>
+   ${ sep }·
 $endfor$
   </div>
   <h1 class="title">$title$</h1>