refactor templates layout

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

layouts/_partials/single/main-body/links.html

@@ -0,0 +1,36 @@
+{{- /*
+  Displays internal and external links for an item
+
+  @params pc  Page context
+  @params sc  Site context
+  */
+-}}
+
+
+<!-- Variable assignment -->
+
+{{- $params := . -}}
+
+
+<!-- Validation -->
+
+{{- if ( not ( isset $params "sc" ) ) -}}
+  {{- errorf "No site context received" -}}
+{{- end -}}
+
+{{- if ( not ( isset $params "pc" ) ) -}}
+  {{- errorf "No page context received (%q)" $params.sc.Page.File.Dir -}}
+{{- end -}}
+
+
+<!-- Rendering -->
+
+<section class="article__links">
+  {{- if $params.pc.Params.internal_links -}}
+    {{- partial "single/main-body/links/internal-links.html" $params -}}
+  {{- end -}}
+
+  {{- if $params.pc.Params.external_links -}}
+    {{- partial "single/main-body/links/external-links.html" $params -}}
+  {{- end -}}
+</section>