refactor templates layout

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

layouts/_partials/media/attr.html

@@ -0,0 +1,62 @@
+<!--
+    Partial to render attribution for a resource.
+
+    @params sc Site context.
+    @params pc Page context.
+    @params attr Resource attribution.
+    @params attr_link  Resource link. Optional.
+    @params attr_license  Resource license. Optional.
+    @params attr_license_link  Resource license link. Optional.
+-->
+
+<!-- Validation -->
+
+{{- if ( not ( isset . "sc" ) ) -}}
+  {{- errorf "No site context received" -}}
+{{- end -}}
+
+{{- if ( not ( isset . "pc" ) ) -}}
+  {{- errorf "No page context received (%q)" .sc.Page.File.Dir -}}
+{{- end -}}
+
+{{- if ( not ( isset . "params" ) ) -}}
+  {{- errorf "No params given (%q)" .pc.File.Path -}}
+{{- end -}}
+
+{{- if ( not ( isset .params "attr" ) ) -}}
+  {{- errorf "No attr given (%q)" .pc.File.Path -}}
+{{- end -}}
+
+<!-- Variable assignment -->
+
+{{- $attr := .params.attr -}}
+{{- $attr_link := .params.attrlink -}}
+{{- $attr_licence := .params.attrlicence -}}
+{{- $attr_licence_link := .params.attrlicencelink -}}
+
+<!-- Rendering -->
+
+<p class="attr">
+  {{- with $attr_link -}}
+    <a href="{{ . }}" target="_blank" rel="noopener">
+  {{- end -}}
+    {{- $attr | safeHTML -}}
+  {{- if $attr_link -}}
+    </a>
+  {{- end -}}
+
+  {{- if $attr_licence }} (
+    {{- $attr_licence_link := partialCached "util/get_licence_link.html" ( dict "licences_data" .sc.Site.Data.licences "licence" $attr_licence "licence_link" $attr_licence_link ) $attr_licence $attr_licence_link -}}
+    
+    {{- with $attr_licence_link -}}
+      <a href="{{- . -}}" target="_blank" rel="noopener">
+    {{- end -}}
+    
+    {{- $attr_licence -}}
+    
+    {{- with $attr_licence_link -}}
+      </a>
+    {{- end -}}
+  )
+  {{- end -}}
+<p>

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>

layouts/_partials/media/picture.html

@@ -0,0 +1,53 @@
+<!--
+    Render an image in a context-appropriate format and size.
+
+    @params src Image media file.
+    @params raw Force raw image only. Optional.
+-->
+
+<!-- Variable assignment -->
+
+{{- $src := .src -}}
+{{- $hint := default ( index $src.Params "hint" ) "" }}
+{{- $format := cond ( and ( isset . "raw" ) .raw ) "" "webp" -}}
+{{- $isResizable := not ( in ( slice "svg" "gif" ) $src.MediaType.SubType ) -}}
+
+
+<!-- Rendering -->
+
+<picture
+  class="picture"
+  itemprop="image"
+>
+  {{ if $isResizable -}}
+    <source 
+      srcset="{{- partialCached "images/get-image.html" ( dict "img" $src "size" "same" "format" $format ) $src.Title -}}"
+    />
+    {{- if gt $src.Width 1200 -}}
+      <source 
+        srcset="{{- partialCached "images/get-image.html" ( dict "img" $src "size" "1200x" "format" $format ) ( printf "%s-1200x" $src.Title ) -}}" 
+        media="(max-width: 1200px)"
+      />
+    {{- end -}}
+    {{- if gt $src.Width 800 -}}
+      <source
+        srcset="{{- partialCached "images/get-image.html" ( dict "img" $src "size" "800x" "format" $format ) ( printf "%s-800x" $src.Title ) -}}"
+        media="(max-width: 800px)"
+      />
+    {{- end -}}
+  {{- end }}
+  <img
+    class="u-photo picture__image"
+    {{ if not $isResizable -}}
+      src="{{- $src.RelPermalink -}}"
+    {{- else -}}
+      src="{{- partialCached "images/get-image.html" ( dict "img" $src "format" $format ) $src.Title -}}" 
+      width="{{- $src.Width -}}"
+      height="{{- $src.Height -}}"
+    {{- end }}
+    {{ with $src.Params.alt -}}alt="{{- . -}}"{{- end }}
+    {{ with $src.Params.title -}}title="{{- . -}}"{{- end }}
+    loading="lazy"
+    role="img"
+  />
+</picture>

layouts/_partials/media/video.html

@@ -0,0 +1,26 @@
+<!--
+    Render a video in an interactive player.
+
+    @params context Video media file.
+    @params page_file_path  Filepath of the calling file for error messages.
+-->
+
+{{- $src := .src -}}
+
+<video
+    class="u-video figure__video"
+    controls
+    itemprop="video"
+    preload="none"
+    src="{{ $src.RelPermalink }}"
+    poster="
+    {{- if $src.Params.poster -}}
+        {{- $posterSrc := $.Page.Resources.GetMatch ( .Get $src.Params.poster ) -}}
+        {{- partialCached "images/get-image.html" ( dict "img" $posterSrc ) $posterSrc.Title -}}
+    {{- else -}}
+        {{- erroridf "a11y-video-poster" "No poster defined for resource %q (%q)" $src.RelPermalink .page_file_path -}}
+    {{- end -}}
+    "
+>
+    Your browser doesn't support embedded video, <a href="{{ $src.RelPermalink }}">view the video here</a>.
+</video>