Fixing 'absolute_url'

site-generator:

    Added all the modules that the script and the templates use to make
    it explicit what is required.

templates/shared-utils.tpl.html:

    Added a new TT² macro called 'absolute_url' which takes two
    arguments, the base and  the path or relative URL. It's fairly
    primitive but seems to work.

templates/content-about.tpl.html,
templates/content-recording.tpl.html,
templates/content-request_a_slot.tpl.html,
templates/content-requested_topics.tpl.html,
templates/page.tpl.html:

    All calls to 'absolute_url' changed to use two arguments, and the
    link definitions adjusted to match this change.

templates/shared-utils.tpl.html

@@ -45,6 +45,20 @@
 <!--% iso8601_date.format(date_to_format) %-->
 <!--% END %-->
 
+<!--% MACRO absolute_url(base, path) BLOCK %-->
+<!--% UNLESS base.empty %-->
+    <!--% UNLESS base.substr(-1) == '/' %-->
+        <!--% base = base _ '/' %-->
+    <!--% END %-->
+<!--% END %-->
+<!--% UNLESS path.empty %-->
+    <!--% IF path.substr(0,1) == '/' %-->
+        <!--% path = path.substr(1) %-->
+    <!--% END %-->
+<!--% END %-->
+<!--% base _ path %-->
+<!--% END %-->
+
 <!--% MACRO absolute_path(baseurl) BLOCK %-->
 <!--% IF baseurl %-->./<!--% ELSE %-->/<!--% END %-->
 <!--% END %-->