add basic support for post translations (#144)

layouts/partials/i18nlist.html

+{{ if .IsTranslated }}
+<h4>{{ i18n "translations" }}</h4>
+<ul class="pl0 mr3">
+    {{ range .Translations }}
+    <li class="list f5 f4-ns fw4 dib pr3">
+        <a class="hover-white no-underline white-90" href="{{ .Permalink }}">{{ .Lang }}</a>
+    </li>
+    {{ end}}
+</ul>
+{{ end }}

layouts/partials/site-navigation.html

       {{ .Site.Title }}
     </a>
     <div class="flex-l items-center">
+      {{ partial "i18nlist.html" . }}
       {{ if .Site.Menus.main }}
         <ul class="pl0 mr3">
           {{ range .Site.Menus.main }}