head: Fix user defining canonical URL resulting in multiple canonical URLs (#133)

* Revert "head: add support for Canonical URLs"

This reverts commit 8af7c551ff.

* Allow user to specify single canonical URL

layouts/partials/head.html

@@ -16,11 +16,7 @@
     {{- .Summary | default (printf "%s - %s" .Title  .Site.Title) }}{{- else }}
     {{- with .Site.Params.description }}{{ . }}{{- end }}{{- end }}{{- end -}}">
 <meta name="author" content="{{ (partial "author.html" . ) }}">
-<link rel="canonical" href="{{ .Permalink }}" />
-{{- $canonical := cond (.IsHome) .Site.Params.canonical .Params.canonical }}
-{{- range $canonical }}
-<link rel="canonical" href="{{ trim . " " }}" />
-{{- end }}
+<link rel="canonical" href="{{ if .Params.canonicalURL -}} {{ .Params.canonicalURL }} {{- else -}} {{ .Permalink }} {{- end }}" />
 {{- if .Site.Params.analytics.google.SiteVerificationTag }}
 <meta name="google-site-verification" content="{{ .Site.Params.analytics.google.SiteVerificationTag }}" />
 {{- end}}