(PDOC-160) Remove the timestamp from output

Prevent mass-changes to files by removing the date in the footer of each page.
Since the generation date isn't particularly useful and isn't tied to either
a git revision or a released version, this could be an easy way to address this
bug.  The files will of-course be regenerated but if there are no changes then
the content will be identical and git will not notice.

lib/puppet-strings/yard/templates/default/layout/html/footer.erb

@@ -0,0 +1,3 @@
+<div id="footer">
+     Generated by <a href="http://yardoc.org" title="Yay! A Ruby Documentation Tool" target="_parent">yard</a>.
+</div>