Opensearch discovery

[bob]

Since we have a search page for each guide it would be nice to let people add it easily to their firefox search button thing. this can be done with stuff we already know.

we need to write out a opensearch.xml like below

<?xml version="1.0" encoding="UTF-8"?>

<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
 <ShortName>$Guide_name</ShortName>
 <Description>Search the $Guide_name</Description>
 <Tags>$guide_name</Tags>
 <Url type="text/html"
      template="$search_url?search={searchTerms}"/>
</OpenSearchDescription>

then we need to add a <link> statement to the header.tt

<link rel="search" href="$guide_url/opensearch.xml""
      type="application/opensearchdescription+xml"
      title="$guide_name" />

[dom]

(In [1096]) Add OpenSearch? description (references #180)

[dom]

(In [1097]) Tweak OpenSearch? description, and add autodiscovery (fixes #180)