Clean up date and timezone handling. We used to pass changelog dates around as a "unixtime timezone" string containing a pair of encoded ints. Now, they get passed around as a (unixtime, timezone) tuple of numbers, which makes much more sense.

#header#
    <title>#repo|escape# Changelog</title>
    <description>#repo|escape# Changelog</description>
    #entries%changelogentry#
  </channel>
</rss>