refactor templates layout

@see https://gohugo.io/templates/new-templatesystem-overview/

layouts/_partials/media/audio.html

@@ -0,0 +1,12 @@
+<!--
+    Render an audio track in an interactive player.
+
+    @params context The audio media file.
+-->
+
+{{- $src := . -}}
+
+<audio class="u-audio figure__audio" itemprop="audio" controls>
+    <source src="{{ $src.RelPermalink }}" type="{{ $src.MediaType }}" />
+    <p>Your browser doesn't support embedded audio, <a href="{{ $src.RelPermalink }}">view the audio here</a>.</p>
+</audio>