Add meta tags for author, and don't allow old `author` param

layouts/partials/author-metadata.html

@@ -0,0 +1,9 @@
+{{ with .Params.authors }}
+
+<meta name="author" content="{{ delimit . ", " }}">
+
+{{ range . }}
+<meta property="article:author" content="{{ . }}">
+{{ end }}
+
+{{ end }}

layouts/partials/head.html

@@ -32,4 +32,6 @@
     {{ template "_internal/schema.html" . }}
 
     <meta name="description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}">
+
+    {{ partial "author-metadata.html" . }}
 </head>

layouts/partials/post-metadata.html

@@ -20,20 +20,10 @@
     {{ end }}
     {{ end }}
 
-    {{ $authorString := "" }}
-
     {{ with .Params.authors }}
-    {{ $authorString = delimit . ", " }}
-    {{ else }}
-    {{ with .Params.author }}
-    {{ $authorString = . }}
-    {{ end }}
-    {{ end }}
-
-    {{ with $authorString }}
     <span class="post-meta-item">
         {{ partial "icon.html" "user-circle" }}
-        {{ . }}
+        {{ delimit . ", " }}
     </span>
     {{ end }}