Add external link feature

Menu entries to internal pages have access to the .Page method, so use
that to discriminate.

layouts/partials/footer_links.html

@@ -2,7 +2,7 @@
 <div class="footer__links">
 	{{ range $key, $value := . }}
 		{{- if ne $key 0 }} | {{ end -}}
-		<a class="footer__link" href="{{ $value.URL }}">{{ $value.Name }}</a>
+		<a class="footer__link" href="{{ $value.URL }}" {{- if not .Page }} target="_blank"{{ end }}>{{ $value.Name }}</a>
 	{{- end }}
 </div>
 {{- end }}

layouts/partials/menu.html

@@ -8,7 +8,7 @@
 		{{- range .Site.Menus.main }}
 		{{- if .Name }}
 		<li class="menu__item{{ if or ($currentNode.IsMenuCurrent "main" .) ($currentNode.HasMenuCurrent "main" .) }} menu__item--active{{ end }}">
-			<a class="menu__link" href="{{ .URL }}">
+			<a class="menu__link" href="{{ .URL }}" {{- if not .Page }} target="_blank"{{ end }}>
 				{{ if .Pre }}
 					{{ readFile (printf "static%s" .Pre) | safeHTML }}
 				{{ end }}