fix: use templater to substitute values in command string
bytes.format() isn't supported on Python 3. Luckily, our template syntax
is similar so we can reuse it. We need a hack to disable \-escapes as '\'
is a directory separator on Windows.
<item>
<title>{branch|escape}</title>
<link>{urlbase}{url|urlescape}rev/{node|short}</link>
<description><![CDATA[{branch|strip|escape|addbreaks}]]></description>
<pubDate>{date|rfc822date}</pubDate>
</item>