templates: Add Twitter Cards, OpenGraph, Schema

This code is licensed under Apache License 2.0
and is part of https://github.com/gohugoio/hugo

layouts/partials/templates/schema.html

@@ -0,0 +1,23 @@
+<meta itemprop="name" content="{{ .Title }}">
+<meta itemprop="description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}">
+
+{{- if .IsPage }}{{ $ISO8601 := "2006-01-02T15:04:05-07:00" }}{{ if not .PublishDate.IsZero }}
+<meta itemprop="datePublished" {{ .PublishDate.Format $ISO8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
+{{ if not .Lastmod.IsZero }}<meta itemprop="dateModified" {{ .Lastmod.Format $ISO8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
+<meta itemprop="wordCount" content="{{ .WordCount }}">
+{{ with $.Params.images }}{{ range first 6 . -}}
+<meta itemprop="image" content="{{ . | absURL }}">
+{{ end }}{{ else -}}
+{{- $images := $.Resources.ByType "image" -}}
+{{- $featured := $images.GetMatch "*feature*" -}}
+{{- if not $featured }}{{ $featured = $images.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
+{{- with $featured -}}
+<meta itemprop="image" content="{{ $featured.Permalink }}">
+{{ else -}}
+{{- with $.Site.Params.images -}}
+<meta itemprop="image" content="{{ index . 0 | absURL }}"/>
+{{ end }}{{ end }}{{ end }}
+
+<!-- Output all taxonomies as schema.org keywords -->
+<meta itemprop="keywords" content="{{ if .IsPage}}{{ range $index, $tag := .Params.tags }}{{ $tag }},{{ end }}{{ else }}{{ range $plural, $terms := .Site.Taxonomies }}{{ range $term, $val := $terms }}{{ printf "%s," $term }}{{ end }}{{ end }}{{ end }}" />
+{{- end }}