Add MACRO media_baseurl

Allow the audio files to be served from a different host

templates/shared-utils.tpl.html

@@ -39,6 +39,12 @@
 <!--% IF baseurl %-->./<!--% ELSE %-->/<!--% END %-->
 <!--% END %-->
 
+<!--% MACRO media_baseurl(baseurl, media_hostname) BLOCK %-->
+<!--% IF media_hostname %-->
+https://<!--% media_hostname %-->/<!--% ELSE %-->
+<!--% baseurl %--><!--% END %-->
+<!--% END %-->
+
 <!--% MACRO step_navigation(baseurl, links, folder) BLOCK %-->
 <!--% IF folder == "" %-->
 <!--% folder = hpr %-->