Added <dc:issued> field to OPDS entries

static/templates/catalog_entries.xml

@@ -1,4 +1,6 @@
-<feed xmlns="http://www.w3.org/2005/Atom" xmlns:opds="http://opds-spec.org/2010/catalog">
+<feed xmlns="http://www.w3.org/2005/Atom"
+      xmlns:dc="http://purl.org/dc/terms/"
+      xmlns:opds="http://opds-spec.org/2010/catalog">
   <id>{{feed_id}}</id>
   <title>{{^filter}}All zims{{/filter}}{{#filter}}Filtered zims ({{filter}}){{/filter}}</title>
   <updated>{{date}}</updated>

static/templates/catalog_v2_entries.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom"
+      xmlns:dc="http://purl.org/dc/terms/"
       xmlns:opds="https://specs.opds.io/opds-1.2"
       xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/">
   <id>{{feed_id}}</id>

static/templates/catalog_v2_entry.xml

@@ -25,6 +25,7 @@
     <publisher>
       <name>{{publisher_name}}</name>
     </publisher>
+    <dc:issued>{{book_date}}</dc:issued>
     {{#url}}
     <link rel="http://opds-spec.org/acquisition/open-access" type="application/x-zim" href="{{{url}}}" length="{{{size}}}" />
     {{/url}}