Implement new template system added with Hugo v0.146.0 (#1858)

* feat(layouts): move all files in layouts/_default up to the layouts/ root.

* feat(layouts): rename layouts/partials folder to layouts/_partials

* feat(layouts): rename layouts/shortcodes folder to layouts/_shortcodes

* feat(taxonomy): add new taxonomy layout template

A template named taxonomy.html used to be a candidate for both Page kind term and taxonomy, now it’s only considered for taxonomy.

layouts/taxonomy.html

@@ -0,0 +1,27 @@
+{{- define "main" }}
+
+{{- if .Title }}
+<header class="page-header">
+    <h1>{{ .Title }}</h1>
+    {{- if .Description }}
+    <div class="post-description">
+        {{ .Description }}
+    </div>
+    {{- end }}
+</header>
+{{- end }}
+
+<ul class="terms-tags">
+    {{- $type := .Type }}
+    {{- range $key, $value := .Data.Terms.Alphabetical }}
+    {{- $name := .Name }}
+    {{- $count := .Count }}
+    {{- with site.GetPage (printf "/%s/%s" $type $name) }}
+    <li>
+        <a href="{{ .Permalink }}">{{ .LinkTitle }} <sup><strong><sup>{{ $count }}</sup></strong></sup> </a>
+    </li>
+    {{- end }}
+    {{- end }}
+</ul>
+
+{{- end }}{{/* end main */ -}}