help frontend caches

Posts do not change often, and can be cached for a long time, by
a frontend RAM cache, by a web accelerator, or by the browser. The
blog's home page may change more often, but still should be cached
by our frontend so that in case a blog is slashdotted loathsxome.cgi
will not be the bottleneck.
there may be more matching posts soon
generate sitemap.xml for loathsxome blogs

Web crawlers like sitemap.xml, so it's good if loathsxome can generate a
full map quickly.

See sitemaps.org for more about sitemap.xml.