add Share Buttons

use Params.ShowShareButtons = true

    credits : https://www.iconfinder.com/iconsets/social-media-rounded-corners
    License:	Free for commercial use

layouts/_default/single.html

@@ -33,6 +33,9 @@
       <li><a href="{{ $href }}">{{ . }}</a></li>
       {{- end }}
     </ul>
+    {{ if .Site.Params.ShowShareButtons }}
+    {{ partial "share-icons.html" . }}
+    {{ end }}
   </footer>
   {{- end }}