Favicons (#54)

* Adding support for favicon

* Fixing html tag

exampleSite/config.toml

   filename = "sitemap.xml"
 
 [params]
+  favicon = ""
   description = "The last theme you'll ever need. Maybe."
   facebook = ""
   twitter = "https://twitter.com/GoHugoIO"

layouts/_default/baseof.html

     {{ end }}
 
     <link href='{{ "dist/main.css" | absURL }}' rel='stylesheet' type="text/css" />
+    {{ block "favicon" . }}
+      {{ partial "site-favicon.html" . }}
+    {{ end }}
 
     {{ if .RSSLink }}
       <link href="{{ .RSSLink }}" rel="alternate" type="application/rss+xml" title="{{ .Site.Title }}" />

layouts/partials/site-favicon.html

+{{ if .Site.Params.favicon }}
+<link rel="shortcut icon" href="/{{ .Site.Params.favicon }}" type="image/x-icon" />
+{{ end }}