templater: register keywords to defaults table
Since the keywords are permanent, there should be no need to pass them
by a temporary mapping.
<item>
<title>{bookmark|escape}</title>
<link>{urlbase}{url|urlescape}rev/{node|short}</link>
<description><![CDATA[{bookmark|strip|escape|addbreaks}]]></description>
<pubDate>{date|rfc822date}</pubDate>
</item>